Printing device

ABSTRACT

A printing apparatus includes an ink ejector, a dryer, and a melting device. The ink ejector ejects an ink to an object on which a printed record is to be produced. The ink contains a medium and a fixing polymer. The dryer heats the object to expedite evaporation of the medium. The melting device is configured to irradiate the ink on the object with ultraviolet rays to subject the ink to heat that causes the fixing polymer to melt and to fix the ink to the object accordingly.

RELATED APPLICATIONS

The present application is a National Phase of International ApplicationNumber PCT/JP2021/023580, filed Jun. 22, 2021, and claims priority basedon Japanese Patent Application No. 2020-112580, filed Jun. 30, 2020.

TECHNICAL FIELD

The present disclosure relates to a printing apparatus.

BACKGROUND OF INVENTION

Various techniques have been proposed for a printing apparatus includingink jet heads. Examples of approaches to fixing ink to an object in ashort time include techniques proposed in Patent Literatures 1 to 3.

Patent Literature 1 discloses ejecting ink to an object and irradiatingthe ink with ultraviolet (UV) rays. The UV rays are absorbed by acoloring agent in the ink, which in turn rises in temperature. The risein temperature expedites the evaporation of solvent in the ink and, byextension, the fixation of the ink (the coloring agent).

Patent Literature 2 discloses a pre-heater and a post-heater as well asa heater configured to heat a long object fed from a roll or, morespecifically, to heat an area on which a printed record is beingproduced. The pre-heater heats part of the object or, more specifically,an area on which a printed record is yet to be produced. The post-heatheats part of the object or, more specifically, an area having a printedrecord produced thereon. Patent Literature 2 also discloses UV lightsources. The UV light sources irradiate the object with UV rays so as tocure ink containing a substance that is polymerized by UV irradiation.

Patent Literature 3 discloses a printing apparatus in which ink isejected onto a transfer belt by ink jet heads and is then applied to anobject by bringing the transfer belt into contact with the object.Patent Literature 3 also discloses a technique for curing a polymer inthe ink by UV irradiation and a technique for causing a binder resin inthe ink to melt through the addition of heat by a heater.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. 2017-30359

Patent Literature 2: Japanese Unexamined Patent Application PublicationNo. 2014-117921

Patent Literature 3: Japanese Unexamined Patent Application PublicationNo. 2014-233864

SUMMARY

According to an aspect of the present disclosure, a printing apparatusincludes an ink ejector, a dryer, and a melting device. The ink ejectoris configured to eject an ink to an object on which a printed record isto be produced. The ink contains a medium and a fixing polymer. Thedryer is configured to heat the object to expedite evaporation of themedium. The melting device is configured to irradiate the ink on theobject with ultraviolet rays to subject the ink to heat that causes thefixing polymer to melt and to fix the ink to the object accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a printing apparatus according to a firstembodiment.

FIG. 2 is a plan view of the printing apparatus in FIG. 1 .

FIG. 3A is a perspective view of an ink jet head included in theprinting apparatus in FIG. 1 , illustrating the ink jet head seenobliquely from above.

FIG. 3B is a perspective view of the ink jet head in FIG. 3A,illustrating the ink jet head seen obliquely from below.

FIG. 3C is a perspective view of a head main body included in the inkjet head in FIG. 3A, illustrating the head main body seen obliquely fromabove.

FIG. 3D is an enlarged view of a region IIId in FIG. 3C.

FIG. 4 is a block diagram illustrating the configuration of a signalprocessing part of the printing apparatus in FIG. 1 .

FIG. 5 is a conceptual diagram illustrating a method by which theprinting apparatus in FIG. 1 enables the fixation of ink.

FIG. 6 is a graph illustrating estimations of the time it takes a mediumin the ink to evaporate.

FIG. 7 is a graph illustrating estimations of the temperaturedistribution in the object subjected to printing performed by theprinting apparatus in FIG. 1 .

FIG. 8A illustrates estimations of temperature variations in a resincontained in the ink heated by UV irradiation.

FIG. 8B illustrates estimations of temperature variations in a resincontained in the ink heated by UV irradiation.

FIG. 9 is a side view of a printing apparatus according to a secondembodiment.

FIG. 10 is a side view of a printing apparatus according to a thirdembodiment.

FIG. 11 is a side view of a printing apparatus according to a fourthembodiment.

FIG. 12A illustrates light absorption properties of an ink set in anembodiment.

FIG. 12B is a schematic diagram for explanation of variations concerningthe ink set.

FIG. 13A illustrates light absorption properties of a UV-absorbing agentcontained in an ink set presented as an example of the variations.

FIG. 13B illustrates light absorption properties of an ink set presentedas an example of the variations.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. The accompanying drawingsare schematic representations. That is, not every detail may beillustrated in the drawings. Constituent elements are not drawn toscale, and the dimension ratios thereof do not fully correspond to theactual dimension ratios. The relative dimensions and the scale ratio mayvary from drawing to drawing. For the purpose of emphasizing aparticular shape or the like, the outline of the shape may beillustrated in such a manner that a specific dimension looks greaterthan it really is.

Embodiments that follow a first embodiment will be principally describedwith a focus on their distinctive features only. Unless otherwise noted,these embodiments may be equated with the previously describedembodiment or may be understood by analogy to the previously describedembodiment. Each element in an embodiment and the corresponding elementin another embodiment may be denoted by the same reference sign,irrespective of possible specific differences therebetween.

The term “medium” may refer to a substance (solvent) used to dissolveanother substance or may refer to a substance (dispersion medium) inwhich particles of another substance (dispersoid) are dispersed. Theterm “dispersion medium” in a narrow sense generally refers to a mediumin which particles (a dispersoid) within a certain size range (e.g.,particles measuring 1 nm or more) are dispersed, whereas the term“dispersion medium” in a broad sense refers to both the dispersionmedium in a narrow sense and the solvent. The dispersion mediummentioned herein is to be understood in a narrow sense.

As is commonly known, a dispersoid is not limited to particles of asolid and may be particles in liquid form or in gaseous form. Unlessotherwise specified, the term “particles” used alone herein refers tonot particles contained as a dispersoid but to particles of a solid.

The term “glass” in a narrow sense generally refers to a substancecontaining silicate as a principal component, whereas the term “glass”in a broad sense refers to an amorphous solid that exhibits a glasstransition as the temperature rises. The glass mentioned herein is to beunderstood in a broad sense. The glass or glass component mentionedherein is not limited to a substance containing silicate as a principalcomponent and may be, for example, a substance containing a polymer as aprincipal component.

As is commonly known, the glass-transition temperature (glass-transitionpoint) is the temperature at which the glass transition occurs. Theglass-transition temperature is hereinafter also referred to as Tg forshort. For example, Tg may be measured as specified in the JapaneseIndustrial Standards (JIS) K7121. Examples of the glass transitiontemperatures specified in JIS K7121 include the extrapolatedglass-transition onset temperature, the mid-point glass-transitiontemperature, and the extrapolated glass-transition end temperature. Tobe more precise, the term “Tg” may be herein understood as the mid-pointglass-transition temperature. When the temperature is kept below Tg, theterm “Tg” may be understood as the extrapolated glass-transition onsettemperature. When the temperature is kept at Tg or higher, the term “Tg”may be understood as the extrapolated glass-transition end temperature.

<First Embodiment>

(Overall Configuration of Printing Apparatus)

FIG. 1 is a side view of a printing apparatus 1 according to a firstembodiment of the present disclosure. FIG. 2 is a plan view of theprinting apparatus 1.

For convenience, the printing apparatus is illustrated with a Cartesiancoordinate system D1-D2-D3 fixed in the space. With regard to theprinting apparatus 1, any direction may be defined as the verticaldirection. For convenience, the +D3 side is deemed as the upper side inthe vertical direction in relation to embodiments of the presentdisclosure. Unless otherwise specified, the terms “plan view” and“seen-through plan view” herein mean that an object of interest isviewed in the direction of the D3 axis.

The printing apparatus 1 conveys an object on which a printed record isto be produced. The object is conveyed from a feed roller 3A to atake-up roller 3B and is hereinafter referred to as an object 101.Various kinds of rollers, such as the feed roller 3A and the take-uproller 3B, constitute a conveyor 5, which conveys the object 101. Theprinting apparatus 1 includes various devices arranged along the path onwhich the object 101 is conveyed. For example, the printing apparatus 1includes an ink ejector 7 and devices (e.g., devices 9, 11, and 13) thatexpedite the process of fixing the ink to the object 101. The inkejector 7 ejects ink droplets to the object 101. The ink ejected by theink ejector 7 lands on the object 101 and is then treated by thedevices. The printing apparatus 1 also include a controller 15 (see FIG.1 ). The controller 15 controls various devices including thosementioned above.

The printing apparatus 1 may additionally include a coater (notillustrated) and a cleaning device. The coater is disposed between thefeed roller 3A and the ink ejector 7 and applies a coating agentuniformly to the object 101. The cleaning device cleans heads 21 of theink ejector 7. The coating agent and the heads 21 will be describedlater.

(Object on Which Printed Record is to be Produced)

For example, the object 101 is in the form of a long sheet. The object101 is winded up by the feed roller 3A prior to printing. The object 101is fed by the feed roller 3A and is conveyed along a path below the inkejector 7. Finally, the object 101 is winded and taken up by the take-uproller 3B. The object 101 may be made of a desired material and may havedesired dimensions (e.g., width, length, and thickness). The object 101may be made of paper, resin, or cloth. The object 101 is a resin film ofdesired thickness. For example, the object 101 is made of polyethyleneterephthalate (PET), and the thickness of the object 101 is not lessthan 5 μm and not more than 20 μm. Ink is ejected onto one of twoopposite surfaces of the object 101. The surface concerned may behereinafter also referred to as a front surface. The other surface maybe hereinafter also referred to as a back surface.

(Ink)

The ink that is yet to be ejected by the ink ejector 7 contains, forexample, a medium (a solvent and/or a dispersion medium), a coloringagent, and at least one kind of polymer. It is required that a fixingpolymer be contained in the ink. Once the ink lands on the object 101,the medium in the ink evaporates. The fixing polymer melts (may betransformed into a vitreous state) by the addition of heat and thensolidifies. The coloring agent is fixed to the object 101 accordingly.

As can be understood from the above description, the ink in the presentembodiment is not a UV curable ink. UV curable inks contain a syntheticresin (a UV curable resin) that is chemically transformed from liquidstate into solid state by reaction with ultraviolet radiation energy.The UV curable resin can be fixed to the object 101 as the UV curableresin is cured. Such a UV curable resin (polymer) is not virtuallycontained in the ink in the present embodiment. However, the UV curableresin may be contained in the ink in the present embodiment, in whichcase the UV curable resin is to be present in an amount that is smallenough to differentiate the ink from UV curable inks.

The constituent that is present in the highest mass % in the ink priorto the ejection of ink is herein referred to as the medium. The mass %of the medium may be set to a desired value. The content of the mediummay be less than 50 mass % or may be not less than 50 mass %. Forexample, the content of the medium is not less than 50 mass % and notmore than 70 mass %. The medium may be water or an aqueous solvent ormay be an organic substance, such as an organic solvent. An example inwhich the medium is water will be mainly described in the presentembodiment.

The coloring agent may be a pigment that is insoluble in the medium, orthe coloring agent may be a dye that is soluble in the medium (solvent).Alternatively, the coloring agent may be a combination of both. Thepigment and dye may be analogous to any of various commonly knownpigments and dyes or any of materials fabricated on the basis of.various commonly known pigments and/or dyes. For example, a pigment(self-dispersing pigment) with a coat that inhibits coagulation is used.Alternatively, an uncoated pigment may be used. The mass % of thecoloring agent in the ink that is yet to be discharged may be set to adesired value. For example, the content of the coloring agent is notless than 1 mass % and not more than 10 mass %.

As can be inferred from the action mentioned above, the fixing polymercontained in the ink in the present embodiment is in the form ofparticles (in solid state) at least before the ink is ejected. Thus, thefixing polymer is insoluble in the medium (e.g., in water). Theglass-transition temperature (Tg) of the fixing polymer is higher thanthe temperature of the ink that is yet to be ejected. The fixing polymerin the ink subjected to heat remains in solid state such that thecoloring agent can be fixed. The fixing polymer may have propertiesother than the property of fixing the coloring agent.

A polymer with a desired Tg may be used as the fixing polymer. Forexample, the ink contains one or more polymers in addition to the fixingpolymer, in which case the fixing polymer may be higher in Tg than someor all of the other polymers. In some embodiments, however, the fixingpolymer is lower in Tg than all of the other polymers. For example, theTg of the fixing polymer is not less than 70° C. and is not more than120° C. (or not more than 110° C.).

The mass % of the fixing polymer may be set to a desired value. Forexample, the ink contains one or more kinds of polymers in addition tothe fixing polymer, in which case the mass % of the fixing polymer maybe higher than the mass % of any one of the other kinds of polymers ormay be higher than the total mass % of all of the other polymers. Thisfeature enhances the effect of causing the medium to evaporate beforethe fixing polymer melts. This effect will be described later. In someembodiments, the mass % of the fixing polymer is lower than the mass %of any one of the other kinds of polymers or is lower than the totalmass % of all of the other polymers. For example, the content of thefixing polymer in the ink that is yet to be ejected is not less than 1mass % and not more than 40 mass %.

The one or more kinds of polymers other than the fixing polymer candecompose and evaporate when heated after the ejection of the ink. Insuch cases, the aforementioned relationship between the mass % of thefixing polymer and the mass % of the one or more kinds of polymers mayhold before the ejection of the ink (before the evaporation). Unlessotherwise specified, the mass % mentioned in relation to variouspolymers in the embodiments refers to the polymer content in a state inwhich the polymers do not evaporate or have yet to evaporate.

A polymer with a desired composition and/or desired constituents may beused as the fixing polymer. For example, the fixing polymer may be anacrylic polymer, a styrene polymer, a vinyl chloride polymer, or amethacrylic acid polymer. The Tg of such a polymer may fall within theaforementioned range; that is, the Tg of such a polymer is not less than70° C. and is not more than 120° C.

The ink may contain, in addition to the fixing polymer, one or morepolymers with desired physical properties and desired functions. Forexample, the ink may contain one or more polymers soluble in the medium(solvent) (e.g., one or more water-soluble polymers) or one or morepolymers insoluble in the medium (solvent) (e.g., one or morewater-insoluble polymers). The one or more polymers that are yet to beejected may be in a liquid or in a solid. A dispersant polymer fordispersing particles of a pigment (i.e., for inhibiting coagulation ofthe pigment) or an abrasion resistant polymer for making the ink highlyresistant to abrasion may be contained in the ink. The mass % of such apolymer may be set to a desired value.

As mentioned above, the one or more polymers may be lower in Tg than thefixing polymer. For example, the dispersant polymer and/or the abrasionresistant polymer may be lower in Tg than the fixing polymer. The Tg ofthe polymer that is lower in Tg than the fixing polymer is not limitedto particular values. For example, the Tg of the polymer is equal to orhigher than 50° C. and is lower than 70° C.

The dispersant polymer may be structurally analogous to commonly knownpolymers. For example, the dispersant polymer is a ribbon-like polymer.In some embodiments, however, the dispersant polymer is in the form ofparticles. The dispersant polymer may include a portion that adsorbs ona pigment and a portion that exhibits its dispersibility. Thedispersibility is exhibited due to, for example, steric hindrance,electrostatic repulsion, and/or obstruction of electrical continuity.The dispersant polymer may be added to an ink containing aself-dispersing pigment although such a dispersant polymer is anon-essential constituent of the ink containing a self-dispersingpigment. The dispersant polymer may be a mixture of styrene and butylacrylate in a 70:30 ratio. The Tg of such a dispersant polymer may fallwithin the aforementioned range; that is, the Tg of such a dispersantpolymer is equal to or higher than 50° C. and is lower than 70° C.

The abrasion resistant polymer may be structurally analogous to commonlyknown polymers. For example, the abrasion resistant polymer may be apolyester resin. The Tg of such an abrasion resistant polymer may fallwithin the aforementioned range; that is, the Tg of such an abrasionresistant polymer is equal to or higher than 50° C. and is lower than70° C.

The ink may contain desired components other than the polymers mentionedabove. For example, the ink may contain a surface-active agent (notincluding the dispersing polymer), a humectant, a surface-tensionmodifier, a PH adjuster, and/or a glazing agent. These additives may bepolymer-based products.

(Conveyor)

The conveyor 5 includes rollers arranged along the path on which theobject 101 is conveyed. For example, the conveyor 5 includes rollersthat are denoted by 3A, 3B, 17A, 17B, and 19A to 19D, respectively. Therollers are each in the form of a hollow cylinder or a solid cylinder,with its axis being orthogonal to the direction of conveyance of theobject 101. The front surface or the back surface of the object 101comes into contact with external circumferential surfaces of the rollersin such a manner that the entire width of the object 101 is within thelength of each roller. Together with or without at least one of therollers, the take-up roller 3B is rotated about the axis by a motor suchthat the object 101 is conveyed. The rollers in the present embodimentare rotated by the motor. In some embodiments, however, the rollers arerotated by another driving source or by manpower.

Any desired number of rollers may be placed in any desired arrangementwith respect to the conveyance path, and each roller may have anydesired diameter. The conveyor 5 in the illustrated example includes, inaddition to the feed roller 3A and the take-up roller 3B, a firsttension roller 19A, a second tension roller 19B, a first heat roller17A, a second heat roller 17B, a third tension roller 19C, and a fourthtension roller 19D, which are arranged in sequence from the position ofthe feed roller 3A to the position of the take-up roller 3B. The rollersexcept for the take-up roller 3B may be driven and rotated by a rolleror the like or may simply turn passively due to friction produced by theobject 101.

The first heat roller 17A and the second heat roller 17B each have thefunction of heating the object 101 and are thus also regarded as devicesthat expedite the process of fixing the ink to the object 101. Thedevices will be described in detail later. The first to fourth tensionrollers denoted by 19A to 19D are involved in application of tension tothe object 101. The first to fourth tension rollers denoted by 19A to19D in the illustrated example bring the object 101 in close contactwith the first heat roller 17A and the second heat roller 17B, thuscontributing to increased efficiency of heat application.

More specifically, the first heat roller 17A is disposed upstream of theink ejector 7 and is in contact with the back surface of the object 101.The second tension roller 19B is disposed upstream of the first heatroller 17A with no other rollers therebetween and is in contact with thefront surface of the object 101, that is, the surface opposite to thesurface with which the first heat roller 17A is in contact. The firsttension roller 19A is disposed upstream of the second tension roller 19Bwith no other rollers therebetween and is in contact with the backsurface of the object 101, that is, the surface opposite to the surfacewith which the second tension roller 19B is in contact. The firsttension roller 19A and/or the second tension roller 19B is subjected toa force exerted by a biasing member (not illustrated), such as a springand/or an actuator, and is thus pushed against the object 101. Theobject 101 is held under tension accordingly. The object 101 is in closecontact with the first heat roller 17A.

The second heat roller 17B is disposed downstream of the ink ejector 7and is in contact with the back surface of the object 101. The thirdtension roller 19C is disposed downstream of the second heat roller 17Bwith no other rollers therebetween and is in contact with the frontsurface of the object 101, that is, the surface opposite to the surfacewith which the second heat roller 17B is in contact. The fourth tensionroller 19D is disposed downstream of the third tension roller 19C withno other rollers therebetween and is in contact with the back surface ofthe object 101, that is, the surface opposite to the surface with whichthe third tension roller 19C is in contact. The third tension roller 19Cand/or the fourth tension roller 19D is subjected to a force exerted bya biasing member (not illustrated), such as a spring and/or an actuator,and is thus pushed against the object 101. The object 101 is held undertension accordingly. The object 101 is in close contact with the secondheat roller 17B.

The first heat roller 17A and/or the second heat roller 17B may have arelatively large diameter. This results in the increased area of closecontact between the object 101 and the heat roller concerned and, byextension, the increased efficiency of heat application. For example,the first heat roller 17A is larger in diameter than the first tensionroller 19A and/or the second tension roller 19B. Likewise, the secondheat roller 17B is larger in diameter than the third tension roller 19Cand/or the fourth tension roller 19D. The first heat roller 17A and/orthe second heat roller 17B may be larger in diameter than any otherrollers of the conveyor 5.

When the object 101 is viewed laterally, a line being a linear edge ofthe object 101 and extending between the second tension roller 19B andthe first heat roller 17A may form an angle with a line being a linearedge of the object 101 and extending between the first heat roller 17Aand the next downstream roller (e.g., the second heat roller 17B in FIG.1 ). The angle of inclination may be relatively large. Thus, the regionin which the object 101 is in close contact with the first heat roller17A extends over an increased angular range about the axis of the firstheat roller 17A. For example, the angle of inclination is not less than45°, not less than 70°, or not less than 90°. The aforementionedrelation holds for a line being a linear edge of the object 101 andextending between the third tension roller 19C and the second heatroller 17B and a line being a linear edge of the object 101 andextending between the second heat roller 17B and the next upstreamroller (e.g., the first heat roller 17A in FIG. 1 ).

The rollers and the like may be placed in varying arrangements. Forinstance, the first heat roller 17A, the first tension roller 19A, andthe second tension roller 19B in the illustrated example may beinstalled in reverse orientation with respect to the surfaces of theobject 101 with which the respective rollers are in contact. It is notrequired that the second tension roller 19B be installed in combinationwith the first tension roller 19A; that is, the first tension roller 19Ais optional. It is not required that the third tension roller 19C beinstalled in combination with the fourth tension roller 19D; that is,the fourth tension roller 19D is optional. In some embodiments, thefirst to fourth tension rollers denoted by 19A to 19D may be eliminated.Rollers other than those illustrated in the accompanying drawings may beprovided. For example, the first heat roller 17A and the second heatroller 17B may be arranged with other rollers disposed therebetween.When viewed laterally, the rollers are arranged along a curve protrudingupward and are in contact with the back surface of the object 101.

The way in which the object 101 is moved may be adjusted as appropriatein accordance with, for example, the workings of the ink ejector 7. Theconveyor 5 may move the object 101 continuously or intermittently. Morespecifically, the object 101 may be moved continuously with theconveyance speed kept constant or varied. The intermittent movement mayalso be regarded as movement with variable speed. The speed ofconveyance of the object 101 may be set to a desired value. For example,the conveyance speed (e.g., the average speed of a variable speedconveyor) is not less than 50 m/min and not more than 300 m/min or isnot less than 100 m/min and not more than 200 m/min.

(Ink Ejector)

The ink ejector 7 includes at least one head. In the illustratedexample, the ink ejector 7 includes twenty heads, which are denoted by21. The heads 21 are oriented toward the object 101 and are directlyengaged in ejection of ink.

The position of the ink ejector 7 may be herein considered synonymouswith the position of the heads 21, the position of an ejection surface21 a, or the location of the region occupied by nozzles 21 b. Theejection surface 21 a and the nozzles 21 b will be described later. Inother words, the term “ink ejector 7” used in relation to the positionof the ink ejector 7 may be replaced with “heads 21”, “ejection surface21 a”, or “region occupied by the nozzles 21 b” where appropriate.

The heads 21 in the present embodiment are essentially fixed in adirection forming an angle with the direction of conveyance of theobject 101; that is, the printing apparatus 1 is a line printer. In someembodiments, the printing apparatus is a serial printer, which ejectsliquid droplets and conveys the object 101 in an alternating manner. Theliquid droplets are ejected from the heads 21 moving in a directionforming an angle with the direction of conveyance of the object 101(e.g., a direction substantially perpendicular to the direction ofconveyance of the object 101).

Each head 21 is held by a member (not illustrated) in such a manner thatthe ejection surface 21 a facing the object 101 is substantiallyparallel to the object 101. The ejection surface 21 a is a surface fromwhich ink is ejected. In the illustrated example, the ejection surface21 a is a lower surface. The distance between the ejection surface 21 aand the object 101 may be set to a desired value. For example, thedistance is not less than 0.5 mm and not more than 20 mm or is not lessthan 0.5 mm and not more than 2 mm. When viewed in plan, the head 21(the ejection surface 21 a) may have a desired planar shape, such as astrip-like shape (or, more specifically, a substantially rectangularshape) whose long sides form an angle with the direction of conveyanceof the object 101. Examples of the direction forming an angle with thedirection of conveyance include a direction substantially perpendicularto the direction of conveyance. The direction concerned may hereinafteralso referred to as a width direction of the object 101.

The heads 21 constitutes at least one head group. Referring to FIG. 2 ,four head groups are provided. The head groups are denoted by 23. Thehead groups 23 each include more than one head 21. In the illustratedexample, the head groups 23 each include five heads 21. The heads 21included in each head group 23 are arranged in such a manner that theirrespective printable ranges lie with no gap therebetween in the widthdirection of the object 101 or in such a manner that peripheral portionsof the printable ranges overlap each other. This arrangement enablesprinting with no blank spaces in the width direction of the object 101.

More specifically, three of the five heads 21 in each head group 23 inthe illustrated example are aligned in the width direction of the object101. The other two of the five heads 21 are aligned in the widthdirection of the object 101 in a manner so as not to be in alignmentwith the three heads 21 in the direction of conveyance and are eachlocated between adjacent ones of the three heads 21 in the widthdirection of the object 101. In other words, the heads 21 in each headgroup 23 are arranged in a staggered pattern.

The four head groups 23 are arranged in the direction of conveyance ofthe object 101. The heads 21 receive a supply of ink from an ink tank 25(see FIG. 1 ). The heads 21 belonging to the same head group 23 receivea supply of ink of the same color. The four head groups 23 enableprinting with inks of four different colors. For example, the headgroups 23 eject magenta (M) ink, yellow (y) ink, cyan (C) ink, and black(K) ink, respectively. These color inks are ejected to the object 101,on which a color image is printed accordingly.

The printing apparatus 1 may include one head 21, in which case an imagewithin the printable range of the head 21 is to be printed inmonochrome. The number of heads 21 in each head group 23 and the numberof head groups 23 may be changed as appropriate, depending on what theobject 101 is like and/or depending on printing conditions. For example,a greater number of head groups 23 enable printing with more colors. Twoor more head groups 23 arranged to eject ink of the same color inalternating manner in the direction of conveyance yield an increase inconveyance speed, with no performance variation between the heads 21.The print area per unit time is increased accordingly. Two or more headgroups 23 arranged in a manner so as not to be in positional agreementin a direction forming an angle with the direction of conveyance toeject ink of the same color yield an increase in resolution in the widthdirection of the object 101.

Instead of color inks, a coating agent in liquid form may be ejecteduniformly or in specific patterns by the heads 21 to surface treat theobject 101. The object 101 may be a low-permeability material, in whichcase the coating agent is to form a liquid receiving layer such that inkcan be readily fixed to the object 101. Alternatively, such a coatingagent is to form a liquid permeation barrier layer such that a liquid isprevented from spreading too much on the high-permeability material (theobject 101) or from mixing too much with another liquid ejected onto anadjacent spot on the high-permeability material (the object 101). Thecoating agent may be applied by using the aforementioned coater (notillustrated) only or both the coater and the heads 21.

The heads 21 may be accommodated in a head chamber (not illustrated).The head chamber is essentially a space isolated from the outside. Thehead chamber has an opening through which the object 101 conveyed by theconveyor 5 enters the head chamber. The head chamber also has an openingthrough which the object 101 conveyed by the conveyor 5 exits the headchamber. The heads 21 apply ink to the object 101 in the head chamber.The head chamber provides greater ease of reducing the range ofvariation of factors affecting the fixation of ink than would bepossible on the outside of the head chamber. Examples of the factorsinclude temperature, humidity, and atmospheric pressure. At least one ofthe various factors in the head chamber may be controlled actively by adesired means.

Ink droplets may be ejected from the heads 21 in a desired manner. Forexample, the heads 21 may each be a piezo head from which ink is ejectedin the form of droplets through the application of pressure by apiezoelectric actuator. Alternatively, the heads 21 may each be athermal head from which ink is ejected in the form of droplets throughthe application of pressure arising from bubbles developed by theaddition of heat to ink.

(Devices That Expedite Process of Fixing Ink to Object on Which PrintedRecord is to be Produced)

As mentioned above, the printing apparatus 1 includes the devices thatexpedite the process of fixing the ink to the object 101. The inkejected by the ink ejector 7 lands on the object 101 and is then treatedby the devices. Examples of the devices include a dryer 9, a meltingdevice, 11, and an auxiliary melting device 13, which are generallylumped together as devices that expedite the fixation of the ink by theaddition of heat to the ink. The devices are in different specificforms, are configured to add different amounts of heat, and/or areplaced in different positions. The devices act differently upon the inkand/or exert influence on their respective actions.

(Dryer)

The dryer 9 expedites the evaporation of the medium in the ink by, forexample, heating the object 101. The dryer 9 heats the object 101 beforeand/or after the ink lands on the object 101. The back surface of theobject 101 may be heated; that is, the ink on the object 101 may beheated indirectly. Alternatively, the front surface of the object 101may be heated; that is, together with the object 101, the ink on theobject 101 may be heated directly. Still alternatively, both the backsurface and the front surface of the object 101 may be heated.

When viewed from another perspective, the dryer 9 may include a portiondisposed upstream of the ink ejector 7 in the direction of conveyance ofthe object 101, a portion in positional agreement with the ink ejector 7in the direction of conveyance, a portion disposed downstream of the inkejector 7 in the direction of conveyance, or at least two of theportions constructed as one piece or discretely located away from eachother. The dryer 9 may also include a portion facing the front surfaceof the object 101 and/or a portion facing the back surface of the object101. For the purpose of ensuring the stable ejection of ink duringheating of the object 101 and the ink, the dryer 9 may include a portionthat is not in positional agreement with the ink ejector 7 and that isdisposed upstream of the ink ejector 7. This reduces the possibilitythat a turbulent flow will be produced in a space that is in positionalagreement with the ink ejector 7.

The position of the dryer 9 may be herein considered synonymous with theposition of a portion directly involved in the heating of the object 101(e.g., the external circumferential surface of the heat roller of thedryer 9 or a warm air vent of the dryer 9) or with the location of aregion being part of the object 101 and being heated by the dryer 9(e.g., a region in contact with the roller or a region at which a jet ofwarm air is directed). In other words, the term “dryer 9” used inrelation to the position of the dryer 9 may be replaced with “portiondirectly involved in the heating” or “region being part of the object101 and being heated” where appropriate.

For example, the dryer 9 heats the object 101 substantially uniformly inthe width direction of the object 101; that is, the amount of heatapplied to the object 101 by the dryer 9 is uniform in the widthdirection. Thus, the temperature distribution of the object 101 issubstantially uniform in the width direction of the object 101. In someembodiments, however, the amount of heat applied to the object 101 bythe dryer 9 is varied in the width direction of the object 101. Forexample, a greater amount of heat may be applied to each side in thewidth direction where heat can dissipate well. The region that can beheated by the dryer 9 at a time may have a desired length in thedirection of conveyance of the object 101.

The dryer 9 may be variously designed. The dryer 9 in the presentembodiment includes the first heat roller 17A. As mentioned above, thefirst heat roller 17A is disposed upstream of the ink ejector 7 and isin contact with the back surface of the object 101.

More specifically, the external circumferential surface of the firstheat roller 17A extends around the axis of the first heat roller 17A andis partially in contact with the object 101. The first heat roller 17Ain an example does not essentially slide over the object 101 and turnsactively or passively as the object 101 moves. The first heat roller 17Ais thus deemed to include a first portion 17 a and a second portion 17b, which are located around the axis of the first heat roller 17A toheat the object 101. The first portion 17 a and the second portion 17 bare deemed to come into contact with the object 101 in an alternatingmanner.

The first heat roller 17A may be in a form that is analogous to any ofvarious commonly known rollers or that is designed on the basis ofvarious commonly known rollers. The first heat roller 17A in an exampleincludes a heating wire therein. When a current flows through theheating wire (not illustrated), the first heat roller 17 generates heatby Joule's law. The first heat roller 17A in another example includes aninduction coil therein and generates heat by induction heating. Thefirst heat roller 17A in still another example includes a channelthrough which a heating medium subjected to heat is supplied from theoutside. The first heat roller 17A includes a base that is in the formof a hollow cylinder or a solid cylinder. The base may be made of aceramic material, metal, and/or any other desired material.

(Melting Device)

The melting device 11 irradiates ink on the object 101 with UV rays toheat the ink. As mentioned above, the fixing polymer (glass component)in the ink subjected to heat melts and then solidifies such that thecoloring agent in the ink is fixed to the object 101. A region beingpart of the object 101 and not being covered with the ink may also beirradiated with UV rays. Some of the UV rays may pass through the ink toradiate into the object 101. The object 101 may be made of a materialthrough which UV rays can essentially pass. Alternatively, the object101 may be made of a material in which heat is produced by absorption ofat least some of the UV rays.

The melting device 11 is disposed downstream of the ink ejector 7 in thedirection of conveyance of the object 101. The melting device 11 islocated on the front surface side of the object 101 and faces the frontsurface. This layout enables the melting device 11 to irradiate the inkwith UV rays. In another example (not illustrated), the melting device11 may be located on the back surface side of the object 101 and facethe back surface of the object 101, in which case an object made of amaterial through which UV rays can pass is to be used as the object 101.Unless otherwise specified, the following description will be based onthe illustrated example layout. The relative positions of (the distancebetween) the ink ejector 7 and the melting device 11 in the direction ofconveyance of the object 101 may be set to a desired value. For example,the ink ejector 7 and the melting device 11 may be disposed with a spacetherebetween or may be adjacent to each other with (almost) no spacetherebetween.

The position of the melting device 11 may be herein consideredsynonymous with the place where UV rays exit the melting device 11(i.e., the position of the foremost part of the optical system) or thelocation of the region that is part of the object 101 and that is to beirradiated with UV rays. In other words, the term “melting device 11”used in relation to the position of the melting device 11 may bereplaced with “place where UV rays exit the melting device 11” or“region that is part of the object 101 and that is to be irradiated withUV rays”.

The object 101 in an example may be irradiated with UV rays emitted bythe melting device 11 after being fully heated by the dryer 9. Whenviewed from another perspective, the fixing polymer in the ink may startmelting while the medium in the ink is evaporating or after the mediumin the ink has completely evaporated. Practically speaking, a very smallamount of medium may be left in the ink at the completion ofevaporation. For example, the medium may be regarded as havingcompletely evaporated when the amount of medium left in the inkimmediately before the UV irradiation is not more than 5 mass %. Therange of not more than 5 mass % may be the percentage content expressedin terms of the mass % of the medium in the ink immediately before theUV irradiation or in terms of the mass % of the medium in the ink thatis yet to be ejected.

The melting device 11 may also be deemed to be disposed downstream ofthe dryer 9 in the direction of conveyance of the object 101. Therelative positions of (the distance between) the dryer 9 and the meltingdevice 11 in the direction of conveyance of the object 101 may be set toa desired value. For example, the dryer 9 and the melting device 11 maybe disposed with a space therebetween or may be adjacent to each otherwith no space therebetween.

For example, a region extending over the entire width of the printablerange of the ink ejector 7 can be irradiated with UV rays emitted by themelting device 11. The melting device 11 extends over the entire widthof the object 101 or over the entire width of the printable range suchthat the region within the width is irradiated with UV rays all at once.In another example (not illustrated), the melting device 11 may bemovable in the width direction of the object 101 such that the regionextending over the entire width of the printable range can be irradiatedwith UV rays emitted by the melting device 11.

For example, the melting device 11 irradiates the object 101 with UVrays substantially uniformly in the width direction of the object 101.That is, the amount of energy of UV rays emitted per unit time to theobject 101 (and the ink) is uniform in the width direction of the object101. The amount of UV rays that can be absorbed by the object 101 (andthe ink) is dependent on the ink distribution in the width direction.Thus, the amount of heat generated by UV irradiation is not necessarilyuniform in the width direction. In some embodiments, however, the amountof UV rays emitted by the melting device 11 is varied in the widthdirection of the object 101.

The region being part of the object 101 and irradiated with UV rays isrectangular and is defined by sides extending in the direction ofconveyance of the object 101 and by sides extending in the widthdirection of the object 101. It is not required that the regionirradiated with UV rays be rectangular. As mentioned above, the regionthat is to be irradiated with UV rays is not smaller in dimension thanthe entire width of the printable range of the ink ejector 7 in thewidth direction of the object 101. The region that is to be irradiatedwith UV rays may have a desired length in the direction of conveyance ofthe object 101.

The melting device 11 may be in any desired form. For example, themelting device 11 includes a light source 11 a, which generates UV rays.The melting device 11 may include, in addition to the light source 11 a,a reflector, a diaphragm, and/or a condenser. The reflector reflects UVrays emitted by the light source 11 a and escaping to the side oppositeto the object 101. The diaphragm has an aperture that is used to adjustthe cross-sectional shape of UV rays. The condenser is a lens thatbrings UV rays into focus. Regardless of whether these elements areincluded in the melting device 11, only the light source 11 a may beregarded as the melting device 11. The light source 11 a may include alight emitting diode (LED), an incandescent lamp, a fluorescent lamp, amercury lamp, or any other desired illuminant. The light source 11 a mayinclude one or more illuminants. For example, the light source 11 a maybe a surface light source made up of multiple illuminants (e.g., LEDs).

As is commonly known, the wavelength of UV radiation is shorter than thewavelength of visible radiation and is, for example, not less than 10 nmand not more than 400 nm. The UV rays emitted by the melting device 11may be near-ultraviolet radiation or far-ultraviolet radiation. Thenear-ultraviolet radiation may be UV-A, UV-B, or UV-C. That is, UV raysof desired wavelength may be emitted by the melting device 11. Theenergy distribution of UV rays emitted by the melting device 11 is in anarrow range of wavelengths. Thus, the UV radiation is similar in thisrespect to laser light. In some embodiments, the energy distribution ofUV radiation emitted by the melting device 11 is in a broad range ofwavelengths. The wavelength may be herein considered synonymous with thewavelength at which the energy is at its (highest) peak.

The melting device 11 may emit UV rays of desired intensity to theobject 101 (and the ink). The intensity of the UV rays herein means theamount of energy of UV rays emitted per unit time per unit area to theobject 101. The UV rays concerned may be more intense than UV raysemitted to an object to cure a UV curable ink on the object. Forexample, the intensity of the UV rays emitted to cure a UV curable inkis generally less than 10 W/cm², whereas the intensity of the UV raysemitted by the melting device 11 may be not less than 10 W/cm², not lessthan 20 W/cm², or not less than 30 W/cm². In some embodiments, however,the UV rays emitted by the melting device 11 is less intense than the UVrays emitted to cure a UV curable ink.

The melting device 11 may emit a desired total quantity of UV rays tothe object 101 (and the ink). The total quantity of radiation isdetermined by integrating the intensity with time. The total quantity ofthe UV radiation concerned may be greater than the total quantity of UVrays emitted to an object to cure a UV curable ink on the object. Forexample, the total quantity of UV rays emitted to an object to cure a UVcurable ink is generally less than 500 mJ/cm², whereas the totalquantity of UV rays emitted to the object 101 by the melting device 11may be not less than 500 mJ/cm², not less than 1000 mJ/cm², not lessthan 1500 mJ/cm², not less than 5000 mJ/cm², or not less than 10000mJ/cm². In some embodiments, however, the total quantity of UV raysemitted to the object 101 by the melting device 11 is less than thetotal quantity of UV rays emitted to an object to cure a UV curable inkon the object.

(Auxiliary Melting Device)

The auxiliary melting device 13 is located opposite the melting device11 with the object 101 placed therebetween. The auxiliary melting device13 heats the back surface of the object 101 to aid in the melting of thefixing polymer. In view of the fact that the auxiliary melting device 13aids in the melting of the fixing polymer, the position of the auxiliarymelting device 13 in the direction of conveyance of the object 101 maybe understood as analogous to the position of the melting device 11 inthe direction concerned. For example, the auxiliary melting device 13may be disposed downstream of the ink ejector 7 and the dryer 9.

The supplemental information provided above in relation to the positionof the dryer 9 holds for the position of the auxiliary melting device13; that is, the position of the auxiliary melting device 13 may beherein considered synonymous with the position of a portion directlyinvolved in the heating of the object 101 or with the location of aregion being part of the object 101 and being heated by the auxiliarymelting device 13. In other words, the term “auxiliary melting device13” used in relation to the position of the auxiliary melting device 13may be replaced with “portion directly involved in the heating” or“region being part of the object 101 and being heated” whereappropriate.

The region being part of the object 101 in a see-through plan view andbeing heated by the auxiliary melting device 13 overlaps the regionbeing part of the object 101 and being irradiated with UV rays emittedby the melting device 11. These two regions may substantially coincidewith each other or may overlap each other. For example, the region beingirradiated with UV rays may coincide with all or part of the regionbeing heated by the auxiliary melting device 13. As can be inferred fromthe action that will be described later, this enables the efficient useof UV radiation energy in the melting of the fixing polymer.

For example, the auxiliary melting device 13 heats the object 101substantially uniformly in the width direction of the object 101; thatis, the amount of heat applied to the object 101 by the auxiliarymelting device 13 is uniform in the width direction. In someembodiments, however, the amount of heat applied to the object 101 bythe auxiliary melting device 13 is varied in the width direction. Forexample, a greater amount of heat may be applied to each side in thewidth direction where heat can dissipate well. The region that can beheated by the auxiliary melting device 13 at a time may have a desiredlength in the direction of conveyance of the object 101.

The auxiliary melting device 13 may be variously designed. The auxiliarymelting device 13 in the present embodiment includes the second heatroller 17B. The first heat roller 17A and/or the second heat roller 17Bmay be structurally the same or different from each other. In eithercase, the aforementioned features of the first heat roller 17A may beadopted into the second heat roller 17B where appropriate; that is, thesecond heat roller 17B may include a first portion and a second portionand may also include a heating wire and/or a channel

(Heads of Ink Ejector)

The heads 21 of the ink ejector 7 may be basically in a form that isanalogous to any of various commonly known heads or that is designed onthe basis of various commonly known heads. The heads 21 in the presentembodiment each may include a heater. The heater heats ink that is yetto be ejected. Heating ink prior to ejection offers the followingadvantage: the medium in the ejected ink can evaporate in a shortertime, and/or the fixing polymer can melt in a shorter time. The heatersincluded in the heads 21 may be in any desired form. The followingdescribes an example of the heaters included in the heads 21.

FIG. 3A is a perspective view of one of the heads 21, illustrating thehead 21 viewed from above (from the side opposite to the side on whichthe object 101 is placed). FIG. 3B is a perspective view of the head 21,illustrating the head 21 viewed from below (from the side on which theobject 101 is placed). FIG. 3C is a perspective view of part of the head21, illustrating a head main body 27 viewed from above.

For example, the head 21 includes the head main body 27 and a backsidemember 29, which is fixed to an upper part of the head main body 27. Thehead main body 27 has the ejection surface 21 a, which is orientedtoward the object 101. The ejection surface 21 a has nozzles 21 b,through which ink droplets are ejected. The head main body 27 is thusregarded as a member that is directly involved in the ejection of inkdroplets. The backside member 29 aids in interconnecting the head mainbody 27 to other constituent components (e.g., the ink tank 25 and thecontroller 15). The head 21 may include, in addition to the head mainbody 27 and the backside member 29, a desired member (e.g., a housingplaced on the backside member 29).

For example, the head main body 27 includes discrete channels and atleast one common channel (not illustrated). Each of the discretechannels is connected to the corresponding one of the nozzles 21 b. Thecommon channel is connected to all of the discrete channels and extendsalong the ejection surface 21 a. The head main body 27 includes at leastone opening, which is denoted by 27 a and is provided in a surfacelocated opposite the ejection surface 21 a. Each opening 27 a isconnected to an end portion of the corresponding common channel or toend portions of two or more common channels. The head 21 in theillustrated example is a piezo head, in which case the head 21 mayinclude an actuator substrate 30. The actuator substrate 30 is locatedopposite the ejection surface 21 a of the head main body 27. Theactuator substrate 30 includes piezoelectric actuators, each of whichapplies pressure to the inside of the corresponding one of the discretechannels.

The backside member 29 includes at least one opening and a channel (notillustrated). The at least one opening is denoted by 29 a and isconnected to the ink tank 25 (not illustrated) with a tube (notillustrated) therebetween. The channel forms a connection between the atleast one opening 29 a and the at least one opening 27 a of the headmain body 27. The backside member 29 includes a driver and a circuitboard therein. The driver (not illustrated) is mounted on the circuitboard (not illustrated) and supplies the head main body 27 (e.g., theactuator substrate 30) with power.

FIG. 3D is an enlarged view of a region IIId in FIG. 3C.

The head main body 27 includes plates 31, which are stacked in layers.Through-holes extending through the plates 31 are constructed as thenozzles 21 b and the channels connected to the nozzles 21 b. The plates31 in an example are made of metal or resin.

Referring to FIG. 3A, the head 21 in such an example includes a heater33A, which is disposed on an upper surface of the backside member 29.The heater 33A may be in sheet form; that is, the heater 33A may be afilm heater. For example, the heater 33A includes a heating wire andinsulators in sheet form. The heating wire is routed in a plane in adesired manner and is sandwiched between the insulators. The heater 33Amay have any desired planar shape and desired dimensions.

In addition to or in place of the heater 33A, a heater 33B may beprovided. Referring to FIG. 3D, the heater 33B is disposed between theplates 31. As with the heater 33A, the heater 33B includes a heatingwire and insulators in sheet form. The heating wire is routed in a planein a desired manner and is sandwiched between the insulators. The heater33B may have any desired planar shape and desired dimensions. In asee-through plan view, the heater 33B may extend across all of thenozzles 21 b.

One or more heaters (not illustrated) may be provided in addition to orin place of the heater on the upper surface of the backside member 29and/or the heater inside the head main body 27. Examples of the heatersinclude a heater (not illustrated) on a side surface of the head 21 (ona surface that forms an angle with the D1 direction or the D2direction), a heater inside the backside member 29, and a heater betweenthe head main body 27 and the backside member 29. It is not requiredthat the heaters be in sheet form. Each heater may be thick enough to bedifferentiated from heaters in sheet form. In addition to or in place ofthe heaters, a channel through which a heating medium flows may beprovided in the head 21.

(Controller)

The controller 15 (see FIG. 1 ) includes a central processing unit(CPU), read-only memory (ROM), random-access memory (RAM), and anexternal storage device, which are not illustrated. In other words, thecontroller 15 includes, for example, a computer. The CPU executesprograms stored in the ROM and/or programs stored in the external deviceto implement various functional units, which will be described later.The controller 15 may include a logic circuit configured to perform onlya certain operation or may include a driver that supplies variouscomponents with power.

In terms of hardware configuration, the controller 15 may be adecentralized controller in a desired form. For example, the controller15 may include subordinate controllers and a superordinate controller.Each of the subordinate controllers is provided for the correspondingone of the conveyor 5, the ink ejector 7, the dryer 9, the meltingdevice 11, and the auxiliary melting device 13. The superordinatecontroller controls (e.g., synchronizes) the subordinate controllers bytransmitting signals to the subordinate controllers and by receivingsignals from the subordinate controllers.

(Configuration of Signal Processing Part)

FIG. 4 is a block diagram illustrating the configuration of a signalprocessing part of the printing apparatus 1.

The controller 15 includes various functional units (e.g., units 35, 37,39, 41, 43, and 45) implemented by the CPU executing the programs. Theunit denoted by 35 controls the heads 21 and is hereinafter referred toas a head control unit. The unit denoted by 37 controls the conveyor 5and is hereinafter referred to as a conveyance speed control unit. Theunit denoted by 39 controls the dryer 9 (the first heat roller 17A) andis hereinafter referred to as a first temperature control unit. The unitdenoted by 41 controls head heaters 33 (the heaters 33A and/or theheaters 33B) of the heads 21 and is hereinafter referred to as a headtemperature control unit. The unit denoted by 43 controls the auxiliarymelting device 13 (the second heat roller 17B) and is hereinafterreferred to as a second temperature control unit. The unit denoted by 45controls the melting device 11 and is hereinafter referred to as a UVcontrol unit 45. Each unit will be described in more detail below.

(Head Control Unit)

The head control unit 35 in an example generates information and thenoutputs the information to the drivers (not illustrated) of the heads21. The information is generated on the basis of data about images andthe like, where characters are regarded as a kind of image. Theinformation concerns the size of droplets that are to be ejected by eachnozzle 21 b at predetermined periodic timings for ejection. Upon receiptof the information, each of the drivers (not illustrated) applies, inaccordance with the information, voltage to driving elements (e.g.,piezoelectric actuators) that are provided for the respective nozzles 21b. The drivers may be regarded as part of the head control unit 35. Theperiodic timings for ejection may be set by the manufacturer of theprinting apparatus 1 and may be invariable. Alternatively, the headcontrol unit 35 may set the periodic timings for ejection on the basisof predetermined information. For example, the predetermined informationconcerns the resolution in the direction of conveyance of the object 101and/or the speed of conveyance of the object 101. The resolution and thespeed are set by the manufacturer or the user. When a printed record isto be produced at a resolution of 1200 dpi by the heads 21 on the object101 conveyed at a speed of 100 m/min, the heads 21 are controlled insuch a way as to operate at a driving frequency of 78.74 kHz to ejectink.

(Conveyance Speed Control Unit)

The conveyance speed control unit 37 controls the conveyor 5 in such amanner that the speed of conveyance of the object 101 is kept at atarget value. The target value essentially remains unchanged while theprinting apparatus 1 is operating. The expression “while the printingapparatus 1 is operating” may be herein read as “during a print job”.The target value may be set by the manufacturer of the printingapparatus 1 and may be invariable. Alternatively, the user may set thetarget value. Still alternatively, the conveyance speed control unit 37may set the target value on the basis of predetermined information. Forexample, the predetermined information concerns the resolution in thedirection of conveyance of the object 101 and/or the periodic ejectiontimings for ejection. The resolution and the periodic timings are set bythe manufacturer or the user.

The conveyance speed control unit 37 in the illustrated example performsfeedback control on the basis of a value acquired from a speed sensor47, which determines the speed of conveyance of the object 101.Alternatively, the conveyance speed control unit 37 may perform openloop control without feedback. The speed sensor 47 may determine thespeed of conveyance of the object 101, or the speed sensor 47 maydetermine the speed of a driving element involved in the conveyance ofthe object 101. The speed sensor 47 in the former case may be analogousto an optical mouse that determines the speed by image recognition. Thespeed sensor 47 in the latter case may be a sensor (e.g., an encoder ora resolver) that detects rotations of the rollers of the conveyor 5 orrotations of the motor driving the rollers. The conveyance of the object101 is synchronized with the ejection of ink from the heads 21accordingly.

The conveyance speed control unit 37 causes a driver (not illustrated)to supply power to at least one motor that rotates at least one of therollers of the conveyor 5. The driver may be regarded as part of theconveyance speed control unit 37. The driver may perform feedbackcontrol (subordinate to the aforementioned feedback control) on themotor or may perform open loop control on the motor.

(First Temperature Control Unit)

The first temperature control unit 39 controls the dryer 9 in such amanner that the temperature of a predetermined portion of the object 101is kept at a target value. For example, the predetermined portion of theobject 101 is a region being heated by the dryer 9. Alternatively, thepredetermined portion may be another region of the object 101 or, morespecifically, a region in which temperature variations are predominantlycaused by the heat liberated from the dryer 9. For example, thepredetermined portion may be disposed downstream of the region beingheated by the dryer 9 and may be a region not being heated by a deviceother than the dryer 9. Referring to FIG. 1 , the predetermined portionmay be a region facing the ink ejector 7.

The target value of the temperature essentially remains unchanged whilethe printing apparatus 1 is operating. The target value may be set bythe manufacturer of the printing apparatus 1 and may be invariable.Alternatively, the user may set the target value. Still alternatively,the first temperature control unit 39 may set the target value on thebasis of predetermined information. Examples of the predeterminedinformation include: information concerning ink and received as an inputfrom the manufacturer or the user (e.g., information that can be used todetermine the Tg of a predetermined polymer); information concerning thespeed conveyance speed set by the manufacturer or the user (the speed ofconveyance of the object 101); and information concerning the relativepositions of (the distance between) the dryer 9 and another device (7,11, 13) and received as an input from the manufacturer or the user.

The first temperature control unit 39 in the illustrated exampleperforms feedback control on the basis of a value acquired from a firsttemperature sensor 49, which determines the temperature of thepredetermined portion of the object 101. Alternatively, the firsttemperature control unit 39 may perform open loop control withoutfeedback. The first temperature sensor 49 may determine the temperatureof the object 101, the ambient temperature of the environment in whichthe object 101 is placed, or the temperature of a desired portion of thedryer 9 (e.g., the temperature of the front surface or the inside of thefirst heat roller 17A). In any case, the first temperature sensor 49 maybe a non-contact temperature sensor or a contact temperature sensor.Examples of the non-contact temperature sensor include radiationthermometers and thermographs. Examples of the contact temperaturesensor include thermocouples, thermistors, and resistance temperaturedetectors. The determined temperature may, as it is, be compared to thetarget value. Alternatively, the determined temperature may be comparedto the target value after a desired correction is made. For example, acomparison may be made after the determined temperature is convertedinto the temperature in a position other than the position of thesensor.

Concrete examples of the control performed on the dryer 9 includecontrol of power that is supplied to a heat generating element (e.g., aheating wire or an induction coil) by way of a driver (not illustrated).What is to be controlled depends on what the heat generating element islike; more specifically, the voltage, the current, and/or the frequency(in the case of controlling AC power) may be controlled. The driver maybe regarded as part of the first temperature control unit 39. Thecontrolled performed on the dryer 9 is not limited to the above. In anembodiment in which a heating medium is supplied to the first heatroller 17A, the flow rate of the heating medium may be controlled.

(Head Temperature Control Unit)

The head temperature control unit 41 controls the head heaters 33 insuch a manner that the temperature of ink in a predetermined portion ofeach head 21 is kept at a target value. The predetermined portion may bethe head main body 27 or the backside member 29 or may be any portion(any channel) in the head main body 27 or in the backside member 29.When the predetermined portion is located in the nozzles 21 b or isclose to the nozzles 21 b, the fixation of an ink 103 to the object 101can be controlled more accurately.

The target value of the temperature essentially remains unchanged whilethe printing apparatus 1 is operating. The target value may be set bythe manufacturer of the printing apparatus 1 and may be invariable.Alternatively, the user may set the target value. Still alternatively,the head temperature control unit 41 may set the target value on thebasis of predetermined information. Examples of the predeterminedinformation include information concerning ink and received as an inputfrom the manufacturer or the user (e.g., information that can be used todetermine the Tg of a predetermined polymer).

The head temperature control unit 41 in the illustrated example performsfeedback control on the basis of a value acquired from a headtemperature sensor 51, which determines the temperature of ink.Alternatively, the head temperature control unit 41 may perform openloop control without feedback. The head temperature sensor 51 may beexposed in a channel to determine the temperature of ink. Alternatively,the head temperature sensor 51 may determine the temperature of theheads 21 without being exposed in a channel. That is, the headtemperature sensor 51 may be a contact temperature sensor exposed in thechannel or a non-contact temperature sensor not exposed in the channelConcrete examples of the contact temperature sensor and concreteexamples of the non-contact temperature sensor have already beenmentioned above. The determined temperature may, as it is, be comparedto the target value. Alternatively, the determined temperature may becompared to the target value after a desired correction is made. Forexample, a comparison may be made after the determined temperature isconverted into the temperature in a position other than the position ofthe sensor.

Concrete examples of the control performed on the head heaters 33include control of power that is supplied to the head heaters 33 by wayof a driver (not illustrated). What is to be controlled depends on whatthe head heaters 33 are like and; more specifically, the voltage, thecurrent, and/or the frequency (in the case of controlling AC power) maybe controlled. The driver may be regarded as part of the headtemperature control unit 41.

(Second Temperature Control Unit)

The second temperature control unit 43 controls the auxiliary meltingdevice 13 in such a manner that the temperature of a predeterminedportion of the object 101 is kept at a target value. For example, thepredetermined portion of the object 101 is a region being heated by theauxiliary melting device 13.

The target value of the temperature essentially remains unchanged whilethe printing apparatus 1 is operating. The target value may be set bythe manufacturer of the printing apparatus 1 and may be invariable.Alternatively, the user may set the target value. Still alternatively,the second temperature control unit 43 may set the target value on thebasis of predetermined information. Examples of the predeterminedinformation include information concerning ink and received as an inputfrom the manufacturer or the user (e.g., information that can be used todetermine the Tg of a predetermined polymer).

The second temperature control unit 43 in the illustrated exampleperforms feedback control on the basis of a value acquired from a secondtemperature sensor 53, which determines the temperature of thepredetermined portion of the object 101. Alternatively, the secondtemperature control unit 43 may perform open loop control withoutfeedback. The second temperature sensor 53 may determine the temperatureof the object 101, the ambient temperature of the environment in whichthe object 101 is placed, or the temperature of a desired portion of theauxiliary melting device 13 (e.g., the temperature of the front surfaceor the inside of the second heat roller 17B). In any case, the secondtemperature sensor 53 may be a non-contact temperature sensor or acontact temperature sensor. Concrete examples of the contact temperaturesensor and concrete examples of the non-contact temperature sensor havealready been mentioned above. The determined temperature may, as it is,be compared to the target value. Alternatively, the determinedtemperature may be compared to the target value after a desiredcorrection is made. For example, a comparison may be made after thedetermined temperature is converted into the temperature in a positionother than the position of the sensor.

The auxiliary melting device 13 may be designed to heat the object 101(and the ink) to a predetermined temperature. For example, thepredetermined temperature is equal to or higher than the Tg of a polymerother than the fixing polymer and is less than the Tg of the fixingpolymer. The melting device 11 may be designed to heat the ink to atemperature higher than the predetermined temperature by UV irradiation.For example, the melting device 11 heats the ink to a temperature higherthan the Tg of the fixing polymer. While the auxiliary melting device 13and the melting device 11 are designed as above, the head applied to theink by the melting device 11 can heavily influence the temperature ofthe object 101. In such a case, the sensor may determine the temperatureof a desired portion of the auxiliary melting device 13, not thetemperature of the object 101. The determined temperature may be used inthe feedback control.

Concrete examples of the control performed on the auxiliary meltingdevice 13 include control of power that is supplied to a heat generatingelement (e.g., a heating wire or an induction coil) by way of a driver(not illustrated). What is to be controlled depends on what the heatgenerating element is like; more specifically, the voltage, the current,and/or the frequency (in the case of controlling AC power) may becontrolled. The driver may be regarded as part of the second temperaturecontrol unit 43. The controlled performed on the auxiliary meltingdevice 13 is not limited to the above. In an embodiment in which aheating medium is supplied to the second heat roller 17B, the flow rateof the heating medium may be controlled.

(UV Control Unit)

The UV control unit 45 in an example controls the melting device 11 insuch a manner that the intensity of UV rays emitted to the object 101 ata constant distance from the melting device 11 is kept at a targetvalue. The distance concerned is the working distance (WD).

The target value of the intensity essentially remains unchanged whilethe printing apparatus 1 is operating. The target value may be set bythe manufacturer of the printing apparatus 1 and may be invariable.Alternatively, the user may set the target value. Still alternatively,the UV control unit 45 may set the target value on the basis ofpredetermined information. Examples of the predetermined informationinclude: information concerning ink and received as an input from themanufacturer or the user (e.g., information that can be used todetermine the Tg of a predetermined polymer); and the temperature of aregion of the object 101 in a hypothetical case in which the region isnot irradiated with UV rays although the region is originally planned tobe irradiated with UV rays. The temperature in the hypothetical case inwhich the region is not irradiated with UV rays may be set by themanufacturer or the user. Alternatively, the UV control unit 45 maycalculate the target value on the basis of predetermined information.Examples of the predetermined information includes: a target value ofthe temperature of (the amount of heat applied by) at least one of thecomponents involved in the application of heat (e.g., the temperature ofat least one of the components denoted by (9 (17A), 21(33), 13(17B));and the relative positions of (the distance between) the melting deviceand the component concerned.

The UV control unit 45 performs open loop control that does not involvefeedback about the intensity of UV radiation. The UV control unit 45also control power that is supplied to the light source 11 a by way of adriver (not illustrated) to enable the light source 11 a to generate UVrays. What is to be controlled depends on what the light source 11 a islike; more specifically, the voltage, the current, and/or the frequency(in the case of controlling AC power) may be controlled. The driver mayperform feedback control of power. The driver may be regarded as part ofthe UV control unit 45.

(Process by Which Ink Is Fixed)

FIG. 5 is a conceptual diagram illustrating a process by which theprinting apparatus 1 enables the fixation of ink to the object 101.

The up-and-down direction and the left-and-right direction in FIG. 5correspond respectively to the up-and-down direction and theleft-and-right direction in FIG. 1 . Part of the object 101 viewed insection is illustrated in FIG. 5 . The object 101 is conveyed from theleft side of the drawing plane to the right side of the drawing plane.The upper left part of the drawing plane is an enlarged sectional viewof part of one of the heads 21. The ink 103 in the form of liquiddroplets are ejected from the head 21 to the (upper) surface of theobject 101. While the ink is moving together with the object 101, thepercentage content and the state (e.g., vitreous state) of eachconstituent of the ink change. FIG. 5 may be regarded as a chronologicalillustration of changes in the state of the same liquid droplet (the ink103) or may be regarded as a simultaneous illustration of differentliquid droplets. The ink is hereinafter denoted by the same numericalsign (103), irrespective of changes in the percentage content and thestate of each constituent of the ink 103.

Referring to FIG. 5 , the state of the ink 103 (the percentage contentand the state of each constituent of the ink 103) is conceptualized asfive different states. These states are hereinafter referred to as firstto fifth states, which are denoted by S1 to S5, respectively.

In the first state S1, the ink 103 retained in the head 21; that is, theink 103 is yet to be ejected. The ink 103 in the first state S1contains, for example, a medium 105 (a solvent and/or a dispersionmedium), a coloring agent 107, and at least one kind of polymer (apolymer 109 and a polymer 111). It is required that a fixing polymer becontained in the ink 103. The polymer denoted by 109 is a fixingpolymer. The polymer denoted by 111 is another example of the at leastone kind of polymer and is hereinafter referred to as a first polymer111. As mentioned above, the ink may contain desired components (e.g.,polymers) other than these polymers. For greater clarity, constituentsother than the polymers 109 and 111 are not illustrated in FIG. 5 . Thedescription about the first polymer 111 may be applicable to otherpolymers.

For convenience, the coloring agent 107 is illustrated as particles(pigments) dispersed in the medium 105. In the first state S1, thefixing polymer 109 is in the form of particles (solid). As mentionedabove, the polymers other than the fixing polymer 109 in the first stateSi each may be a dissolved substance or a dispersoid and may be a liquidor a solid. The first polymer 111 is illustrated as a ribbon-likedispersant polymer. As mentioned above, the accompanying drawings areschematic representations. Thus, the diameter and the density ofparticles in FIG. 5 do not fully correspond to the actual diameter andthe actual density of particles in the ink 103.

In the second state S2, the ink 103 ejected from the head 21 flies inthe air toward the object 101; that is, the ejected ink is yet to landon the object 101. The second state S2 (the percentage content and thestate of each constituent) is not basically different from the firststate S1.

Once the ink 103 lands on the object 101, the ink 103 remains in thethird state S3 for a certain period of time. In this state, the medium105 gradually evaporates. The heat applied to the ink 103 beforehand bythe head heaters 33 expedites the evaporation of the medium 105. Theheat applied to the object 101 by the dryer 9 and transferred to the ink103 also expedites the evaporation of the medium 105.

Polymers (not illustrated) other than the fixing polymer 109 may be inthe form of particles in both the first state Si and the second state S2and may, in part or in whole, be vitrified in the third state S3. One ormore kinds of polymers other than the fixing polymer 109 may decomposeand evaporate by the application of heat. Additives other than thepolymers may remain in the ink or may evaporate.

In the fourth state S4, the ink 103 is about to be irradiated with UVrays emitted by the melting device 11. The medium 105 in this state isat a more advanced stage of evaporation than in the third state S3. Forexample, the medium 105 may be at the completion of evaporation. As aresult of evaporation of the medium 105, a substance dissolved in themedium 105 or a dispersoid in the medium 105 (except for those havingevaporated) coagulates and is left. FIG. 5 illustrates the process bywhich the coloring agent 107 and the fixing polymer 109 coagulate.

One or more kinds of polymers (e.g., the first polymer 111) other thanthe fixing polymer 109 may be left or may decompose and evaporate. Eachpolymer left in the ink is or is not in a vitreous state. For example,the polymers left in the ink except for the fixing polymer 109 may, inwhole, be in a vitreous state. For greater clarity, the fourth state S4and the fifth state S5 in FIG. 5 are illustrated without the firstpolymer 111, regardless of the presence or absence of the first polymer111 in the ink 103.

In the fifth state S5, the ink 103 is irradiated with UV rays emitted bythe melting device 11. In this state, the coloring agent 107 generatesheat by absorption of UV rays, and as a result, the fixing polymer 109melts (is vitrified). In the subsequent state (not illustrated), thetemperature of the ink 103 decreases after the irradiation of UV rays.Consequently, the fixing polymer 109 solidifies, causing the coloringagent 107 to adhere to the object 101. The other polymers (e.g., thefirst polymer 111), if present in the ink 103, also solidify (or remainin solid state) although the other polymers are not illustrated.

As mentioned above, the medium 105, in part or in whole, may evaporatebefore the fixing polymer 109 melts. This reduces the possibility thatthe fixing polymer 109 in a vitreous state will be formed into a coatingthat can inhibit the evaporation of the medium 105. The medium 105 canthus evaporate in an efficient manner. When the content of the medium105 in the first state Si serves as a reference amount, the amount ofevaporation of the medium 105 before the fixing polymer 109 melts(before the application of heat through UV irradiation) is, for example,not less than 30 mass %, not less than 50 mass %, or not less than 70mass % or is the total amount of the medium 105 (i.e., not less than 95%or 100 mass %).

The application of heat to the ink 103 through UV irradiation enablesthe ink 103 to rise in temperature in a short time and to cause thefixing polymer 109 to melt accordingly. On the downside, heat isgenerated mainly in the coloring agent 107, that is, in a localizedmanner. Thus, heating the ink 103 solely by UV irradiation can result inan excessive temperature rise in a particular part, and the quality ofthe ink 103 and/or the object 101 can deteriorate accordingly.Additional application of heat to the object 101 by the dryer 9 and/orthe auxiliary melting device 13 offers the following advantages: theheat generation is less localized; and the time it takes to raise thetemperature is shortened.

Paradoxically speaking, a determination whether the polymer concerned isthe fixing polymer 109 may be made on the basis of the presence orabsence of the aforementioned action, not by its chemical composition.One or more kinds of polymers in the ink 103 may be in solid form(particles) before the application of heat through UV irradiation andmay melt (be vitrified) by UV irradiation. Such a polymer left in theink 103 and remaining in solid state may be regarded as the fixingpolymer 109.

(Target Temperature That is to be Achieved by Using Head Heaters)

As mentioned above, the heads 21 may include the head heaters 33 suchthat the ink 103 in the first state Si is maintained at a predeterminedtarget temperature. The first state S1 (the percentage content and thestate of each constituent) may be basically the same or similar to thestate of the ink 103 at room temperature (e.g., 20° C.). For example,the target temperature that is to be achieved by using the head heaters33 is lower than the Tg of any or all kinds of polymers that are notsupposed to be vitrified in the ink at room temperature. Conversely, theTg of any or all kinds of polymers in the ink 103 is higher than thetarget temperature that is to be achieved by using the head heaters 33.Setting the target temperature and/or the Tg to satisfy the abovecondition reduces the possibility that a molten polymer will adhere to,for example, inner surfaces of the nozzles 21 b.

The target temperature that is to be achieved by using the head heaters33 may be as high as possible without being equal to or exceeding the Tgof any or all kinds of polymers in the ink. Conversely, the Tg of any orall kinds of polymers in the ink 103 may be as low as possible whilebeing higher than the target temperature that is to be achieved by usingthe head heaters 33. Setting the target temperature and/or the Tg tosatisfy the condition as above reduces the length of time from when theink 103 lands on the object 101 and to when the ink 103 is fixed to theobject 101. Unintended spreading of liquid droplets on the object 101 isless likely to occur; that is, the liquid droplets can retain theirshape well. One of the findings based on experiments conducted by theinventors in the present application was that increasing the temperatureof the ink 103 (e.g., to 45° C. or above) improves the shape retentioncapability of the ink 103.

An example of the Tg of any or all kinds of polymers in the ink and anexample of the target temperature that is to be achieved by using thehead heaters 33 are as follows. The Tg of any or all kinds of polymersin the ink may be higher than 50° C. The target temperature that is tobe achieved by using the head heaters 33 may be higher than or equal to40° C. and lower than 50° C. or may be equal to or higher than 40° C.and equal to or lower than lower 45° C. Given that the targettemperature that is to be achieved by using the heads 21 is lower thanthe Tg of a specific kind of polymer in the ink 103 (e.g., the Tg of thedispersant polymer or the Tg of the abrasion resistant polymer), thedifference between the target temperature and the Tg of the polymerconcerned may be equal to or higher than 1° C. and equal to or lowerthan 10° C. or may be equal to or higher than 1° C. and equal to orlower than 5° C.

The temperature of the ink 103 decreases in the second state S2 in whichthe ink 103 (the ejected liquid droplets) flies in the air. Thetemperature varies linearly with the distance (time period) over whichthe ink flies in the air. The amount of decrease in temperature isrelatively small. Examples of estimations are as follows. In a case inwhich two picoliters (2 pL) of liquid droplets fly over a distance of 1mm at an initial speed of 10 m/s in an atmosphere at 25° C., liquiddroplets initially at a temperature of 40° C. cools to 38.0° C., andliquid droplets initially at a temperature of 50° C. cool to 46.6° C. Ina case in which ten picoliters (10 pL) of liquid droplets fly over adistance of 1 mm at an initial speed of 10 m/s in an atmosphere at 25°C., liquid droplets initially at a temperature of 40.0° C. cool to 39.3°C., and liquid droplets initially at a temperature of 50° C. cool to48.8° C. The temperature differential may be taken into consideration ormay be disregarded in the course of setting the target temperature thatis to be achieved by using the head heaters 33 and/or in the course ofsetting a target temperature that is to be achieved by using the dryer9.

(Target Temperature That is to be Achieved by Using Dryer)

As mentioned above, the dryer 9 may maintain the object 101 at thetarget temperature. The temperature of the object 101 may be consideredto be substantially equal to the temperature of the ink 103 in the thirdstate S3. In this paragraph and the following paragraph, the targettemperature that is to be achieved by using the dryer 9 may thus be readas the temperature of the ink 103 in the third state S3. The targettemperature may be lower than the Tg of the fixing polymer 109.Conversely, the Tg of the fixing polymer 109 in the ink 103 is higherthan the target temperature that is to be achieved by using the dryer 9.Setting the target temperature and/or the Tg to satisfy the abovecondition reduces the aforementioned possibility that the fixing polymer109 in a molten state will be formed into a coating that can inhibit theevaporation of the medium 105.

The target temperature that is to be achieved by using the dryer 9 maybe as high as possible without exceeding the Tg of the fixing polymer109. For example, the target temperature that is to be achieved by usingthe dryer 9 may be set in such a manner that the temperature of theobject 101 at the instant when the ink 103 lands on the object 101 ishigher than the temperature of the ink 103. This feature furtherexpedites the evaporation of the medium 105. Conversely, the Tg of thefixing polymer 109 in the ink 103 may be as low as possible while beinghigher than the target temperature that is to be achieved by using thedryer 9. The fixing polymer 109 can melt in a shorter time accordingly.

The time it takes the medium 105 to evaporate may be taken intoconsideration in the course of setting the target temperature that is tobe achieved by using the dryer 9.

FIG. 6 is a graph illustrating estimations of the time it takes themedium 105 to evaporate. The horizontal axis of the graph represent thesurface temperature T(° C.) of the ink 103 in the form of droplets. Thevertical axis of the graph represent the time t (s) it takes the medium105 in the ink 103 to evaporate.

Calculations are performed given that the ink 103 in the form of liquiddroplets are hemispherical water droplets each having a surface area ofabout 3.8×10⁻¹⁰ m² and being exposed to an atmosphere at 25° C.

As can be seen in the graph, the time t plumets at the instant when thetemperature T exceeds the atmospheric temperature. Thereafter, the timet becomes substantially constant when the temperature T is about toreach the boiling point (about 70° C.). In a state (not illustrated inFIG. 6 ) in which the temperature T is equal to the atmospherictemperature (25° C.), the time t stands at about 4000 s. The resultslead to the following conclusion: the target temperature that is to beachieved by using the dryer 9 is preferably set to, for example, 70° C.

The following describes concrete examples of the Tg of the fixingpolymer 109 and concrete examples of the target temperature that is tobe achieved by using the dryer 9. In this paragraph, the targettemperature that is to be achieved by using the dryer 9 may be read asthe temperature of the ink 103 in the third state S3. The Tg of thefixing polymer may be equal to or higher than 70° C. and equal to orlower than 120° C. Given that the target temperature that is to beachieved by using the dryer 9 is lower than the Tg of the fixing polymer109, the target temperature may be equal to or higher than 50° C. andlower than 120° C., may be equal to or higher than 60° C. and lower than120° C., or may be equal to or higher than 70° C. and lower than 120° C.Given that the Tg of the fixing polymer 109 is higher than the targettemperature that is to be achieved by using the dryer 9, the differencebetween the Tg of the fixing polymer 109 and the target temperature maybe equal to or higher than 1° C. and equal to or lower than 50° C., maybe equal to or higher than 1° C. and equal to or lower than 30° C., andmay be equal to or higher than 1° C. and equal to or lower than 10° C.Unless a contradiction or the like arises, any of the concrete examplesof the numerical range may be combined with the concrete example of theTg of the polymer other than the fixing polymer 109 and with theconcrete example of the target temperature that is to be achieved byusing the head heaters 33.

The dryer 9 in the present embodiment is functionally synonymous withthe first heat roller 17A. The object 101 cools as it moves away fromthe first heat roller 17A. Given this, the target temperature mentionedabove may be a target temperature in a predetermined position betweenthe first heat roller 17A and the ink 103 on the verge of landing(between the first heat roller 17A and the ink ejector 7). For example,the predetermined position may be the position of the first heat roller17A or may be immediately anterior to the ink ejector 7. The targetvalue of the temperature in the predetermined position may be set insuch a manner that the temperature in the entirety of a region beingpart of the object 101 and extending from the position of the first heatroller 17A to immediately anterior to the ink ejector 7 falls within theaforementioned range of the target temperature.

The following describes examples of estimations of the temperaturedistribution in the object 101.

Conditions (assumptions) for the estimations are as follows. The firstheat roller 17A is at a temperature of 50° C. (Case 1), 60° C. (Case 2),and 70° C. (Case 3). The second heat roller 17B is at a temperature of70° C. The influence of the melting device 11 is disregarded. The object101 is placed in an atmosphere at 25° C. The object 101 is conveyed at aspeed of 100 m/min. The object 101 is made of PET and has a thickness of12 μm.

FIG. 7 is a graph illustrating the estimations. The horizontal axis ofthe graph represents the position x(m) in the D1 direction. The verticalaxis of the graph represents the temperature T(° C.) of the object 101.The position of the first heat roller 17A is denoted by x1. The positionof the second heat roller 17B is denoted by x2. Lines denoted by LT50,LT60, and LT70 represent the estimations in the cases in which the firstheat roller 17A is at a temperature of 50° C., 60° C., and 70° C.,respectively.

As can be seen in the graph, the temperature of the object 101 decreasessubstantially linearly. It is therefore easy to estimate the temperatureof the object 101 (the ink 103) in the position of a device other thanthe dryer 9 (e.g., the ink ejector 7 or the melting device 11) on thebasis of the temperature of (the amount of heat applied by) the dryer 9(the first heat roller 17A in the present embodiment), the relativepositions of (the distance between) the dryer 9 and the device concerned(e.g., the ink ejector 7 or the melting device 11), and the speed ofconveyance of the object 101. The distance and the conveyance speed maybe regarded as the time it takes to convey the object 101 from the dryer9 to the device concerned.

When viewed from another perspective, the aforementioned parameters(e.g., the amount of applied heat, the distance, and the conveyancespeed) may be specified with desired values (target values) such thatdesired temperatures are achieved in desired positions. The variouseffects mentioned above can be produced accordingly. For example, thetemperature in a region being part of the object 101 and beingimmediately anterior to a region facing the ink ejector 7 may be equalto or higher than the Tg of the first polymer 111 and lower than the Tgof the fixing polymer 109. The temperature in a region being part of theobject 101 and extending from immediately posterior to the dryer 9 (thefirst heat roller 17A in the present embodiment) to immediately anteriorto a region facing the melting device 11 may be equal to higher than theTg of the first polymer 111 and lower than the Tg of the fixing polymer109. The medium can fully evaporate before the melting device 11 causesthe fixing polymer 109 to melt.

Referring to FIG. 7 , the temperature in a region at a distance of 1.5 mdownstream of the first heat roller 17A is maintained substantially ator above 40° C. when the first heat roller 17A is at or above 60° C. or,more specifically, at or above 70° C. That is, the temperature T ismaintained at such a relatively high level over a relatively longdistance (a relatively long time period). This reduces the possibilitythat the temperature of the ink 103 on the object 101 will fall. It isthus easier to enable the shape retention of the ink 103 and/or moreexpeditious evaporation of the medium through the addition of heat tothe ink 103.

(Target Temperature That is to be Achieved by Using Auxiliary MeltingDevice)

As mentioned above, the auxiliary melting device 13 may maintain theobject 101 at a target temperature. The auxiliary melting device 13 maybe designed to heat the object 101 to the predetermined temperaturebelow the Tg of the fixing polymer 109 as mentioned above. When the headapplied by the melting device 11 can heavily influence the temperatureof the object 101, the target temperature that is to be achieved byusing the auxiliary melting device 13 may be the temperature of apredetermined portion of the auxiliary melting device 13, rather thanthe temperature of the object 101.

Where appropriate, the target temperature that is to be achieved byusing the auxiliary melting device 13 may be understood as analogous tothe target temperature that is to be achieved by using the dryer 9. Forexample, the target temperature that is to be achieved by using theauxiliary melting device 13 may be lower than the Tg of the fixingpolymer 109 and may be as high as possible without exceeding the Tg ofthe fixing polymer 109. Given that the target temperature that is to beachieved by using the auxiliary melting device 13 is lower than the Tgof the fixing polymer 109, the target temperature may be equal to orhigher than 50° C. and lower than 120° C., may be equal to or higherthan 60° C. and lower than 120° C., or may be equal to or higher than70° C. and lower than 120° C. In other words, given that the Tg of thefixing polymer 109 is higher than the target temperature that is to beachieved by using the auxiliary melting device 13, the differencebetween the Tg of the fixing polymer 109 and the target temperature maybe equal to or higher than 1° C. and equal to or lower than 50° C., maybe equal to or higher than 1° C. and equal to or lower than 30° C., andmay be equal to or higher than 1° C. and equal to or lower than 10° C.

(UV Irradiation by Melting Device)

As mentioned above, the temperature in a region being part of the object101 (the ink 103) and located immediately anterior to the melting device11 may be set to a desired value, and/or the temperature in a regionbeing part of the object 101 (the ink 103) and heated by the auxiliarymelting device 13 may be set to a desired value. The intensity of UVrays emitted by the melting device 11 and the irradiation time (theirradiation distance in the D1 direction) may be set to desired valuesto ensure that the temperature of the fixing polymer 109 can be heatedto its Tg or above.

The following describes examples of estimations of the temperature risecaused by UV irradiation.

The temperature rise in resin containing carbon black (pigment) servingas the coloring agent 107 is estimated. Conditions (assumptions) for theestimations are as follows. Particles of the coloring agent 107 are 70nm cubes. The coloring agent 107 has a concentration of 2200 kg/m³. Thecoloring agent 107 has a specific heat of 691 J/kgK. As the coloringagent 107, 5200 particles are contained in 0.8 pL of resin. The resinhas a concentration of 1060 kg/m³. The resin has a specific heat of 1340J/kgK. The intensity of UV irradiation is 352 kW/m², 80% of which is tobe converted into heat. Heat is to be trapped in the resin. The initialtemperature prior to UV irradiation is set to 25° C. (Case 1) and 50° C.(Case 2).

FIG. 8A is a graph illustrating temperature variations in the 0.8 pL ofresin under the aforementioned conditions. The horizontal axis of thegraph represents the UV irradiation time t (μs). The vertical axis ofthe graph represents the temperature T(° C.). Temperature variationswith the initial temperature at 25° C. are denoted by a broken line, andtemperature variations with the initial temperature at 50° C. aredenoted by a solid line.

As can be seen in the graph, the temperature of the resin containing thecoloring agent 107 reached and exceeded the Tg of the fixing polymer 109in a relatively short time. More specifically, the temperature of theresin increases from 50° C. to 120° C. in about 0.01 s.

The temperature rise in water containing the resin is estimated.Conditions (assumptions) for the estimations are as follows. The ink isa mixture of 1.2 pL of water and the 0.8 pL of resin (in which 5200particles are contained as the coloring agent 107). The water has aconcentration of 1000 kg/m³. The water has a specific heat of 4180J/kgK. Heat is to be trapped in the ink. The initial temperature priorto UV irradiation is set to 25° C. (Case 1) and 50° C. (Case 2).

FIG. 8B is a graph illustrating temperature variations in the water (inthe whole of the ink) under the aforementioned conditions. Thehorizontal axis of the graph represents the UV irradiation time t (μs).The vertical axis of the graph represents the temperature T(° C.).Temperature variations with the initial temperature at 25° C. aredenoted by a broken line, and temperature variations with the initialtemperature at 50° C. are denoted by a solid line.

As can be seen in the graph, the temperature of the ink reached andexceeded the Tg of the fixing polymer 109 in a relatively short time.More specifically, the temperature of the ink increases from 50° C. to120° C. in about 0.05 s.

In this way, the temperature of the ink can be estimated from theintensity of UV irradiation and the irradiation time. This means thatthe intensity of UV irradiation and the irradiation time (theirradiation distance in the D1 direction) can be set in such a mannerthat the ink 103 heated (to a temperature below the Tg of the fixingpolymer 109) by the dryer 9 and/or the auxiliary melting device 13 isfurther heated in the fifth state S5 to a desired temperature (e.g., toa temperature equal to or higher than the Tg of the fixing polymer 109).

It was found from the example estimations that the ink 103 can be heatedto a desired temperature in a relatively short time (e.g., in 0.05 s orless) by means of UV irradiation.

According to the example estimations, it takes about 0.05 s to heat theink 103 to 120° C., whereas it takes about 0.01 s to heat the mixture ofresin and the coloring agent 107 to 120° C. This indicates that the UVirradiation causes a local temperature rise. When viewed from anotherperspective, hating the ink 103 by using not only the melting device 11but also the dryer 9 and/or the auxiliary melting device 13 can reducethe local temperature increase.

(Example Dimensions of Devices)

The printing apparatus 1 and various devices included in the printingapparatus 1 may have desired dimensions, and the relative positions of(the distance between) the devices may be set as desired. The ink 103 inthe present embodiment is dried and fixed to the object 101 in anefficient manner. This feature makes it easier to shorten the entirelength of the printing apparatus 1 or, more specifically, the distancebetween the ink ejector 7 and the take-up roller 3B. The dimensions mayfall within the following ranges. These ranges are examples; that is,the dimensions may fall outside these ranges.

The entire length of the printing apparatus 1 in the (D1) direction inwhich the object 101 is conveyed may be not less than 1 m and not morethan 5 m. The distance between the axis of the feed roller 3A and theaxis of the first heat roller 17A in the D1 direction may be not lessthan 200 mm and not more than 600 mm. The diameter of the first heatroller 17A (and the second heat roller 17B) may be not less than 20 mmand not more than 100 mm. The distance between the axis of the firstheat roller 17A and the front end of the ink ejector 7 in the D1direction may be not less than 200 mm and not more than 600 mm. Thedistance between the front end of the ink ejector 7 and the rear end ofthe ink ejector 7 in the D1 direction may be not less than 300 mm andnot more than 900 mm. The distance between the rear end of the inkejector 7 and the front end of the melting device 11 or the axis of thesecond heat roller 17B in the D1 direction may be not less than 200 mmand not more than 600 mm. The distance between the front end of themelting device 11 and the rear end of the melting device in the D1direction may be not less than 5 mm and not more than 30 mm. Given thata cooler (not illustrated) that cools the object 101 (the ink 103) isprovided, the distance between the rear end of the melting device 11 andthe axis of the take-up roller 3B in the D1 direction may be not lessthan 300 mm and not more than 900 mm. The speed of conveyance of theobject 101 is not less than 50 mm/min and not more than 300 mm/min, inwhich case the conveyance speed is compatible with the aforementioneddimensional ranges.

The present embodiment described above can be summarized as follows. Theprinting apparatus 1 includes the ink ejector 7, the dryer 9, and themelting device 11. The ink ejector 7 ejects the ink 103 to the object101. The ink 103 contains the medium 105 and the fixing polymer 109. Thedryer 9 heats the object 101 to expedite evaporation of the medium 105.The melting device 11 irradiates the ink 103 on the object 101 withultraviolet rays to subject the ink 103 to heat that causes the fixingpolymer 109 to melt and to fix the ink 103 (the coloring agent 107) tothe object 101 accordingly.

For example, a device dedicated to the purpose of causing the medium 105to evaporate and a device dedicated to the purpose of transforming thefixing polymer 109 into a molten state may be included in the printingapparatus. This leads to the speeding-up of the process of fixing theink 103, the enhanced efficiency of fixing the ink 103, and/or theimproved quality of the ink 103 or the like. More specifically, thedryer 9 heats the object 101. Heating the object 101 in advance beforethe ink 103 lands on the object 101 enables the ink 103 to rise intemperature immediately upon contact with the object 101, thus causingthe medium 105 to start evaporating. The melting device 11 causes thecoloring agent 107 to rise in temperature by UV irradiation, and thefixing polymer 109 is heated accordingly. That is, the fixing polymer109 is heated before the applied heat is transferred to the object 101.This results in improved thermal efficiency. Heating the ink 103 notonly by UV irradiation but also by using the dryer 9 reduces thepossibility that the quality of the ink 103 and/or the object 101 willdeteriorate due to excessive heating of a particular part. This approachalso reduces the possibility the object 101 will wrinkle and/or becomedeformed due to localized heating. As stated above, localized heatingcan cause wrinkles and/or deformation. This is one of the findings basedon experiments conducted by the inventors in the present application.

The melting device 11 may be disposed downstream of the dryer 9 in thedirection of conveyance of the object 101. When viewed from anotherperspective, the melting device 11 may cause the fixing polymer 109 tomelt after the dryer 9 causes the medium 105 to evaporate.

For example, the melting device 11 causes the fixing polymer 109 to meltafter the medium 105 at least partially evaporates. As mentioned above,this feature reduces the possibility that the fixing polymer 109 in amolten state will be formed into a coating that can inhibit theevaporation of the medium 105. The ink 103 can be dried and fixed in ashort time accordingly.

The amount of heat to be applied to the object 101 by the dryer 9 (thetarget temperature that is to be achieved by using the dryer 9), therelative positions of (the distance between) the dryer 9 and the meltingdevice 11, and the speed of conveyance of the object 101 may be set tovalues at which the medium 105 fully evaporates through the applicationof heat by the dryer 9 before the melting device 11 causes the fixingpolymer 109 to melt.

This feature further reduces the possibility that the fixing polymer 109will be formed into a coating that can inhibit the evaporation of themedium 105. This feature also reduces the possibility that bubbles willbe formed in the fixing polymer 109 due to the evaporation of the medium105. Thus, the ink 103 will be in higher quality after being fixed. Morespecifically, the development of bubbles that would cause a reduction ofgloss can be inhibited.

The printing apparatus 1 may include the auxiliary melting device 13.The auxiliary melting device 13 may be located opposite the meltingdevice 11 with the object 101 placed between the auxiliary meltingdevice 13 and the melting device 11. The auxiliary melting device 13 mayheat the back surface of the object 101 to aid in the melting of thefixing polymer 109. The back surface is opposite to the surface to whichthe ink 103 is ejected.

That is, the front surface of the object 101 is heated through UVirradiation, and the back surface of the object 101 is heated by theauxiliary melting device 13. This feature enables the object 101 to risein temperature in a short time. It is still possible to cause the fixingpolymer 109 to melt by means of UV irradiation only. Although such anapproach falls within the technical scope of the present disclosure, thefeature mentioned above is more advantageous in terms of reducing anexcessive temperature rise in a particular part of the ink 103 and, byextension, the possibility that the ink 103 and/or the object 101 willdiminish in quality.

The auxiliary melting device 13 may have a heating surface maintained ata predetermined temperature during contact with the back surface of theobject 101. The heating surface may be an external circumferentialsurface of the second heat roller 17B. In other words, the auxiliarymelting device 13 may heat the object 101 to the predeterminedtemperature. The melting device 11 may heat the ink on the object 101 toa temperature above the predetermined temperature.

Hating the object 101 to the predetermined temperature by using theauxiliary melting device 13 provides ease of reducing the possibility ofan excessive temperature rise in a particular part. The amount of heatto be applied to the object 101 is adjusted by the auxiliary meltingdevice 13 in accordance with variations in the atmosphere in which theobject 101 is placed. This eliminates the need to adjust the intensityof UV irradiation or the irradiation time. This feature simplifies themechanism (control) by which UV irradiation causes the ink 103 to risein temperature above the Tg of the fixing polymer 109.

The dryer 9 may include the first portion 17 a and the second portion 17b designed to repeatedly come into contact with the object 101 in analternating manner to heat the object 101.

It is still possible to heat the object 101 by using a plate-like heaterthat slides over the object 101 (a plate-like heater in a continualcontact with the object 101). Although such an approach falls within thetechnical scope of the present disclosure, the feature mentioned aboveis more advantageous in the following respect: heat loss caused by thecontact with the object 101 can be at least partially compensated for bya temperature rise in the first portion 17 a or the second portion 17 bwhile it is not in contact with the object 101. As a result, the amountof heat production per unit volume of a heat-producing part of theheating wire or the like may be reduced, and the object 101 may beheated at a constant rate. The load borne by the heat-producing part maybe reduced accordingly.

The dryer 9 may heat the object 101 to a temperature below theglass-transition temperature (Tg) of the fixing polymer 109. The meltingdevice 11 may heat the ink 103 on the object 101 to a temperature equalto or higher than the Tg of the fixing polymer 109.

Through the addition of heat by the dryer 9 designed as above, thefixing polymer 109 hardly melts or only a little amount of the fixingpolymer 109 melts. As a workaround, the melting device 11 causes thefixing polymer 109 to melt without fail. This feature further reducesthe possibility that the fixing polymer 109 will be formed into acoating that can inhibit the evaporation of the medium 105.

The ink 103 may contain the first polymer 111 different from the fixingpolymer 109. The dryer 9 may heat the object 101 to a temperature equalto or higher than the glass-transition temperature (Tg) of the firstpolymer 111 and lower the glass-transition temperature (Tg) of thefixing polymer 109.

This means that the temperature of the ink 103 heated by the dryer 9 maybe relatively high within a range not exceeding the Tg of the fixingpolymer 109. Thus, the dryer 9 further expedites the evaporation of themedium 105, as mentioned above.

The dryer 9 may include a first dryer disposed upstream of the inkejector 7 in the (D1) direction in which the object 101 is conveyed. Inthe present embodiment, the first dryer is the first heat roller 17A.The amount of heat to be applied by the first dryer, the relativepositions of the first dryer and the ink ejector 7, and the speed ofconveyance of the object 101 may be set by the manufacturer, the user,and/or the controller 15 to values at which the temperature in a regionbeing part of the object 101 and being immediately anterior to a regionfacing the ink ejector 7 is equal to or higher than the Tg of the firstpolymer 111 and lower than the Tg of the fixing polymer 109.

When the temperature in the region being part of the object 101 andbeing immediately anterior to the ink ejector 7 is lower than the Tg ofthe fixing polymer 109, the temperature of the ink 103 landing on theregion will be less likely to reach the Tg of the fixing polymer 109.This feature provides ease of reducing the possibility that the fixingpolymer 109 will be formed into a coating that can inhibit theevaporation of the medium 105. Meanwhile, the temperature in the regionbeing part of the object 101 and being immediately anterior to the inkejector 7 is relatively high. Thus, the ink 103 landing on the regionwill rise in temperature in a short time, and the evaporation of themedium 105 will be expedited accordingly.

The dryer 9 may be disposed upstream of the melting device 11 in thedirection of conveyance of the object 101. The amount of heat to beapplied by the dryer 9 (the target temperature that is to be achieved byusing the dryer 9), the relative positions of (the distance between) thedryer 9 and the melting device 11, and the speed of conveyance of theobject 101 is conveyed may be set by the manufacturer, the user, and/orthe controller 15 to values at which the temperature in a region beingpart of the object 101 extending from immediately posterior to the dryer9 to immediately anterior to a region facing the melting device 11 isequal to or higher than the Tg of the first polymer 111 and lower thanthe Tg of the fixing polymer 109.

When the temperature in the region being part of the object 101 andextending from immediately posterior to the dryer 9 to immediatelyanterior to the melting device 11 is lower than the Tg of the fixingpolymer 109, the fixing polymer 109 is less likely to be formed into acoating in the region concerned. Thus, the evaporation of the medium 105is less likely to be inhibited by the coating. Meanwhile, thetemperature in the region being part of the object 101 is relativelyhigh. Thus, the evaporation of the medium 105 will be further expeditedaccordingly.

The first polymer 111 may be a dispersant polymer.

The dispersant polymer is dispersed in the medium 105 up to the timewhen the medium 105 fully evaporates. The dispersant polymer is thusless likely to be formed into a coating. For example, the dryer 9 heatsthe ink 103 to a temperature higher than the Tg of the dispersantpolymer, in which case the possibility that the evaporation of themedium 105 will be inhibited by a coating is lower than in the casewhere the dryer 9 heats the ink 103 to a temperature higher than the Tgof the fixing polymer. Thus, this feature enhances the effect of heatingthe ink 103 to a relatively high temperature before the fixing polymer109 is formed into a coating; that is, the medium 105 can evaporate in amore efficient manner.

The glass-transition temperature of the fixing polymer 109 may be higherthan the glass-transition temperature of any other polymer contained inthe ink 103.

This means that the Tg of the fixing polymer 109 may be relatively high.The ink 103 may thus be heated by the dryer 9 to a relatively hightemperature within a range not exceeding the Tg of the fixing polymer.Thus, this feature further expedites the evaporation of the medium 105before the fixing polymer 109 is formed into a coating.

<Second Embodiment>

FIG. 9 is a side view of a printing apparatus 201 according to a secondembodiment and is analogous to FIG. 1 relevant to the first embodiment.

The melting device 11 included in the printing apparatus 201 is disposeddownstream of the second heat roller 17B in the direction conveyance ofthe object 101. In other words, the printing apparatus 201 does notinclude the auxiliary melting device 13 facing the melting device 11with the object 101 placed between the auxiliary melting device 13 andthe melting device 11. The first heat roller 17A and the second heatroller 17B constitute a dryer 209, which is disposed upstream of themelting device 11. That is, the dryer 209 includes a first dryer and asecond dryer that are the first heat roller 17A and the second heatroller 17B, respectively.

Unless a contradiction arises, the control performed on the first heatroller 17A (the first dryer) in the present embodiment may be understoodas analogous to the control performed on the first heat roller 17A (thedryer 9) in the first embodiment. Likewise, the target temperature thatis to be achieved by using the first heat roller 17A (the first dryer)in the present embodiment may be understood as analogous to the targettemperature that is to be achieved by using the first heat roller 17A(the dryer 9) in the first embodiment. In the present embodiment, theterm “dryer 9” mentioned in relation to the previous embodiment may bereplaced with “dryer 209” or “first dryer” unless a contradictionarises.

Unless a contradiction arises, the control performed on the second heatroller 17B (the second dryer) in the present embodiment may beunderstood as analogous to the control performed on the first heatroller 17A (the dryer 9) in the first embodiment. Likewise, the targettemperature that is to be achieved by using the second heat roller 17B(the second dryer) in the present embodiment may be understood asanalogous to the target temperature that is to be achieved by using thefirst heat roller 17A (the dryer 9) in the first embodiment. In thepresent embodiment, the terms “dryer 9” and “first heat roller 17A”mentioned in relation to the previous embodiment may be replacedrespectively with “second dryer” and “second heat roller 17B” unless acontradiction arises. At the same time or alternatively, the followingmay hold. Unless a contradiction arises, the control performed on thesecond heat roller 17B (the second dryer) in the present embodiment maybe understood as analogous to the control performed on the second heatroller 17B (the auxiliary melting device 13) in the first embodiment.Likewise, the target temperature that is to be achieved by using thesecond heat roller 17B (the second dryer) in the present embodiment maybe understood as analogous to the target temperature that is to beachieved by using the second heat roller 17B (the auxiliary meltingdevice 13) in the first embodiment. In the present embodiment, the term“auxiliary melting device 13” mentioned in relation to the previousembodiment may be replaced with “second dryer” unless a contradictionarises.

For example, the amount of heat to be applied to the object 101 by thedryer 209 or the second heat roller 17B (the second dryer), the relativepositions of the dryer 209 or the second heat roller 17B and the meltingdevice 11, and the speed of conveyance of the object 101 is conveyed maybe set to values at which the medium 105 fully evaporates through theapplication of heat by the dryer 209 or the second heat roller 17Bbefore the melting device 11 causes the fixing polymer 109 to melt. Theamount of heat to be applied by the dryer 209 or the second dryer, therelative positions of the second dryer and the melting device 11, andthe speed of conveyance of the object 101 may be set to values at whichthe temperature in a region being part of the object 101 and extendingfrom immediately posterior to the dryer 209 (from immediately posteriorto the second dryer) to immediately anterior to a region facing themelting device 11 is equal to or higher than the Tg of the first polymer111 and lower than the Tg of the fixing polymer 109.

As in the previous embodiment, the present embodiment described aboveinvolves the following feature. The printing apparatus 1 includes theink ejector 7, the dryer 209, and the melting device 11. The ink ejector7 ejects the ink 103 to the object 101. The ink 103 contains the medium105 and the fixing polymer 109. The dryer 209 heats the object 101 toexpedite evaporation of the medium 105. The melting device 11 irradiatesthe ink 103 on the object 101 with ultraviolet rays to subject the ink103 to heat that causes the fixing polymer 109 to melt and to fix theink 103 (the coloring agent 107) to the object 101 accordingly.

This feature produces effects equivalent to those produced in the firstembodiment. More specifically, a device dedicated to the purpose ofcausing the medium 105 to evaporate and a device dedicated to thepurpose of transforming the fixing polymer 109 into a molten state maybe included in the printing apparatus. This leads to the speeding-up ofthe process of fixing the ink 103, the enhanced efficiency of fixing theink 103, and/or the improved quality of the ink 103 or the like.

As described above in relation to the present embodiment, the dryer 209may include the first dryer (the first heat roller 17A) and the seconddryer (the second heat roller 17B) disposed upstream and downstream,respectively, of the ink ejector 7 in the direction of conveyance of theobject 101. The melting device 11 may be disposed downstream of thesecond dryer.

Heating the object 101 in advance by using the first heat roller 17Abefore the ink 103 lands on the object 101 enables the ink 103 to risein temperature quickly upon contact with the object 101. Heating theobject 101 by using the second heat roller 17B after the ink 103 landson the object 101 enables the medium 105 to evaporate quickly. It isthus easy to cause the medium 105 to evaporate fully before beingirradiated with UV rays emitted by the melting device 11.

The first embodiment is more advantageous than the second embodiment inthe following respects. The second heat roller 17B can contribute moreto the process by which the temperature of the fixing polymer 109 isincreased to its Tg or above. The workload of the melting device 11 canbe further lightened accordingly. Supposing the distance between the inkejector 7 and the second heat roller 17B is unchangeable due toconstraints on the mechanism design, the first embodiment providesgreater ease of shortening the entire length of the printing apparatus 1than the second embodiment.

<Third Embodiment>

FIG. 10 is a side view of a printing apparatus 301 according to a thirdembodiment and is analogous to FIG. 1 relevant to the first embodiment.

The printing apparatus 301 includes more than one melting device. In theillustrated example, the printing apparatus 301 includes three meltingdevices, which are denoted by 11A, 11B, and 11C, respectively. Themelting devices 11A, 11B, and 11C each may be basically identical orsimilar to the melting device 11 in the first embodiment (except fordesign specifications, such as dimensions). The melting devices may behereinafter also simply denoted by 11 (without A to C) when there is noneed to distinguish one from another. The three melting devices 11 maybe regarded as one melting device.

The melting devices 11 are in different positions in the direction ofconveyance of the object 101. Regions being part of the object 101 andirradiated with UV rays emitted by the respective melting devices 11 maybe discretely located away from each other in the conveyance direction,may be adjacent to each other with substantially no gap therebetween inthe conveyance direction, or may overlap each other in the conveyancedirection.

The melting devices 11 are arranged along a region where the object 101is bent with its front surface being curved convexly by the second heatroller 17B. The melting devices 11 irradiate mostly the curved regionwith UV rays in directions normal to the respective portions of thecurved region of the object 101. That is, the curved region of theobject 101 is irradiated with UV rays emitted in multiple directionsnormal to the curved region. Referring to FIG. 10 , the curved region ofthe object 101 is irradiated with UV rays emitted by the three meltingdevices, namely, the melting devices 11A, 11B, and 11C. Alternatively,more than three melting devices 11 at a greater distance from the object101 may be disposed to irradiate the curved region of the object 101with UV rays. As mentioned above, a region being part of the object 101and curved convexly is irradiated with UV rays, in which case a largenumber of melting devices 11 may be disposed to irradiate a particularregion of the object 101 with UV rays at nearly right angles to theregion. This feature enables an increase in the energy density of UVirradiation such that the fixing polymer 109 can melt in a short time.

In another example (not illustrated), the melting devices 11 arearranged along a linear region of the object 101 to irradiate the linearregion with UV rays. In the previous example, UV rays are emitted to theobject 101 to irradiate a region that is bent with its surface beingcurved convexly. The region concerned may be bent by a roller other thanthe second heat roller 17B or may be bent by two or more rollers.

In another example (not illustrated), the curved region of the object101 may be irradiated with UV rays emitted in multiple directions normalto the curved region without using multiple melting devices 11. In thiscase, one melting device 11 may extend along the curved region of theobject 101. More specifically, two or more light sources 11 a may bearranged along the curved region of the object 101, and a reflector, adiaphragm, and/or a power supply circuit may be disposed in such amanner as to be shared with the light sources 11 a. The reflector and/orthe diaphragm may be shaped in conformance with the curved region of theobject 101. The light sources 11 a may be provided for the respectivemelting devices 11. In this case, the reflector, the diaphragm, and/orthe power supply may be regarded as being shared by the melting devices11. Alternatively, one melting device 11 including a surface lightsource may be disposed. In this case, the surface light source, which isan example of the light source 11 a, is curved and include LEDs arrangedalong the curved region of the object 101. The LEDs are also examples ofthe light source 11 a.

The two or more melting devices 11 may be identical to each other ordifferent from each other in terms of specifics concerning thewavelength of UV rays, the intensity of UV rays, and/or how long aregion being part of the object 101 and irradiated with UV rays at atime is in the conveyance direction.

For example, some or all of the melting devices 11 may be configured toemit UV rays of the same wavelength. The region that can be irradiatedwith UV rays at a time by the melting devices 11 concerned may be longerin the direction of conveyance of the object 101 than the region thatcan be irradiated with UV rays at a time by one melting device 11. It istherefore possible to convey the object 101 at a faster speed while thetime period over which UV rays are emitted to the same spot on theobject 101 is long enough to cause the fixing polymer 109 to melt. Whenviewed from another perspective, this feature increase the designflexibility needed to ensure that the irradiation distance (time) of themelting devices 11 is long enough to cause the fixing polymer 109 tomelt.

Alternatively, some or all of the melting devices 11 may be configuredto emit UV rays of different wavelengths. UV rays of a certainwavelength can be absorbed in a greater amount by the ink; that is,irradiating the ink with UV rays of a certain wavelength enablesgeneration of a greater amount of heat, where the wavelength concernedvaries depending on the color of the ink 103 (the kind of the coloringagent 107). This will be described later in relation to variations ofthe ink. When being a color printer, the printing apparatus 1 mayinclude melting devices 11 provided for the respective colors andconfigured to emit UV rays of wavelengths at which a greater amount ofheat can be generated. In this case, inks 103 of different colors can beheated uniformly.

As with the melting devices configured to irradiate the curved region ofthe object 101 with UV rays, the melting devices 11 (light sources 11 a)that emit UV rays of different wavelengths may share a reflector, adiaphragm, and/or a power supply circuit and may be regarded as onemelting device. LEDs (examples of the light sources 11 a) configured toemit UV rays of different wavelengths and arranged mixedly mayconstitute one surface light source, which is an example of the lightsources 11 a.

As in the previous embodiments, the present embodiment described aboveinvolves the following feature. The printing apparatus 301 includes theink ejector 7, the dryer 9, and the melting device 11. This featureproduces effects equivalent to those produced in the first embodiment.More specifically, a device dedicated to the purpose of causing themedium 105 to evaporate and a device dedicated to the purpose oftransforming the fixing polymer 109 into a molten state may be includedin the printing apparatus. This leads to the speeding-up of the processof fixing the ink 103, the enhanced efficiency of fixing the ink 103,and/or the improved quality of the ink 103 or the like.

The printing apparatus 301 may include the conveyor 5 configured toconvey the object 101 and to bend at least part of the object 101 beingconveyed. The surface to which the ink 103 is ejected is curvedconvexly. One or more melting devices 11 may emit UV rays to a regionbeing part of the object 101 and bent by the conveyor 5 or, morespecifically, by the second heat roller 17B.

With the external circumference side being greater in area than theinternal circumference side, the region in which or more melting devices11 are disposed is greater than the region being part of the object 101and irradiated with UV rays. A relatively small region in the object 101may thus be irradiated with UV rays emitted in multiple directionsnormal to the region. This feature enables an increase in the energydensity such that the ink 103 can rise in temperature in a short time.The region that can be irradiated with UV rays extends not only in theD1 direction but also in other directions. This feature makes it easierto shorten the length of the printing apparatus 1.

The printing apparatus 301 may include a plurality of light sources 11 aconstituting one or more melting devices 11. The plurality of lightsources 11 a are configured to emit UV rays of different wavelengths.

When being a color printer as in the case mentioned above, the printingapparatus 301 may include light sources 11 a provided for the respectivecolors and configured to emit UV rays of wavelengths at which a greateramount of heat can be generated. In this case, inks 103 of differentcolors can be heated uniformly. This feature reduces the possibilitythat a specific ink 103, namely, an ink of a specific color will beheated too much or too little. Thus, the inks 103 and/or the object 101will be in higher quality. When viewed from another perspective, thefunction of causing the fixing polymer 109 to melt is less dependent onthe color of the ink 103. In other words, the mechanism that governs themelting of the fixing polymer 109 can be adapted for various printingapparatuses, such as monochrome printers and color printers.

<Fourth Embodiment>

FIG. 11 is a side view of a printing apparatus 401 according to a fourthembodiment and is analogous to FIG. 1 relevant to the first embodiment.

The printing apparatus 401 includes a dryer 409, which is analogous tothe dryer 209 in the second embodiment in the following respect: thedryer 409 includes a first dryer (the first heat roller 17A) disposedupstream of the ink ejector 7 and a second dryer disposed between theink ejector 7 and the melting device 11. The second dryer in the presentembodiment is denoted by 410 and is configurationally different from thesecond dryer (the second heat roller 17B) in the second embodiment.

More specifically, the second dryer 410 may be a warm air dryer thatejects a jet of warm air to the object 101. The second dryer 410 in theillustrated example includes a front dryer 455A and a back dryer 155B.The front dryer 455A ejects a jet of warm air to the front surface ofthe object 101, and the back dryer 455B ejects a jet of warm air to theback surface of the object 101. The front dryer 455A and the back dryer455B may be hereinafter also simply referred to as dryers 455 when thereis no need to distinguish one from another. The second dryer 410 mayinclude the front dryer 455A or the back dryer 455B only.

For example, the dryers 455 each include a heat source and a blower (notillustrated). Gas around the heat source is blown out by the blower. Theheat source may be similar to the first heat roller 17A; that is, theheat source may be a heating wire, an induction coil, or a channelthrough which a heating medium flows. The blower may include a fan and amotor that rotates the fan. The dryers 455 each may include a ductthrough which the gas flown out by the fan flows to the object 101. Inanother example (not illustrated), one heat source may be provided, andgas around the heat source may be guided by a duct to both the frontsurface and the back surface of the object 101. The gas blown out to theobject 101 may be air.

Unless a contradiction arises, the control performed on the dryer 409 orthe second dryer 410 in the present embodiment may be understood asanalogous to the control performed on the dryer 9 (the first heat roller17A) in the first embodiment and/or the control performed on the seconddryer (the second heat roller 17B) in the second embodiment. Likewise,the target temperature that is to be achieved by using the dryer 409 orthe second dryer 410 in the present embodiment may be understood asanalogous to the target temperature that is to be achieved by using thedryer 9 (the first heat roller 17A) in the first embodiment and/or thetarget temperature that is to be achieved by using the second dryer (thesecond heat roller 17B) in the second embodiment.

For example, the amount of heat to be applied to the object 101 by thedryer 409 or the second dryer 410, the relative positions of the dryer409 or the second dryer 410 and the melting device 11, and the speed ofconveyance of the object 101 may be set to values at which the medium105 fully evaporates through the application of heat by the dryer 409 orthe second dryer 410 before the melting device 11 causes the fixingpolymer 109 to melt. The amount of heat to be applied by the dryer 409or the second dryer 410, the relative positions of the second dryer 410and the melting device 11, and the speed of conveyance of the object 101may be set to values at which the temperature in a region being part ofthe object 101 and extending from immediately posterior to the dryer 409(from immediately posterior to the second dryer 410) to immediatelyanterior to a region facing the melting device 11 is equal to or higherthan the Tg of the first polymer 111 and lower than the Tg of the fixingpolymer 109.

As with the other dryers, the second dryer 410 may be subjected to openloop control or feedback control. When the feedback control isperformed, the temperature sensor configured to determine thetemperature of the object 101 may determine the temperature of theobject 101 itself, the ambient temperature of the environment in whichthe object 101 is placed, or the temperature of a desired portion of thesecond dryer 410. When the second dryer 410 is a warm air dryer, thetemperature sensor may be configured to determine the temperature of gasblown out to the object 101.

As with the other dryers, the second dryer 410 may be subjected tocontrol of power that is supplied to the heat sources. When the seconddryer 410 is a warm air dryer, control of amount of air that is blownout may be performed in addition to or in place of the control of powerthat is supplied to the heat sources.

As in the previous embodiments, the present embodiment described aboveinvolves the following feature. The printing apparatus 401 includes theink ejector 7, the dryer 409, and the melting device 11. This featureproduces effects equivalent to those produced in the first embodiment.More specifically, a device dedicated to the purpose of causing themedium 105 to evaporate and a device dedicated to the purpose oftransforming the fixing polymer 109 into a molten state may be includedin the printing apparatus. This leads to the speeding-up of the processof fixing the ink 103, the enhanced efficiency of fixing the ink 103,and/or the improved quality of the ink 103 or the like.

The dryer 409 (the second dryer 410) may include a warm air dryer thatblows out heated gas. The second dryer is simpler in this case than inthe second embodiment, in which the second dryer is the second heatroller 17B. Meanwhile, higher energy efficiency is achieved in thesecond embodiment. The reason for this is that dissipation of heat fromthe object 101 is inhibited more in the second embodiment than in thepresent embodiment

(Variations Concerning Ink Set)

Given that inks 103 of different colors are included in an ink set andare to be irradiated with UV rays of the same wavelength, the followingdescribes variations concerning the ink set. With regard to thefollowing variations, the ink set is intended for use with a colorprinter including one or more melting devices 11 (one or more lightsources 11 a) that emit UV rays of the same wavelength. The variationsconcerning the ink set may be adopted into a color printer capable ofemitting UV rays of different wavelengths.

FIG. 12A is a graph schematically illustrating light absorptionproperties of inks 103 in an example in which the inks 103 are ofdifferent colors. FIG. 12A concerns the inks 103 in the embodimentsdescribed above, not the inks 103 in the variations.

The horizontal axis of the graph represents the wavelength λ (in unitsof nm). The vertical axis of the graph represents the absorbance Abs,which is a dimensionless quantity. RU denotes the UV wavelength range.RV denotes the visible light wavelength range. RI denotes the infraredwavelength range. LY denotes a line representing the properties of anink 103 or, more specifically, of a yellow ink. LM denotes a linerepresenting the properties of an ink 103 or, more specifically, of amagenta ink. LC denotes a line representing the properties of an ink 103or, more specifically, of a cyan ink. LK denotes a line representing theproperties of an ink 103 or, more specifically, of a black ink. Thegraph deals with inks of four different colors with the same opticalpath length.

The absorbance may be the common logarithm (the logarithm with base 10)of the ratio of the intensity of incident light to the intensity ofemitted light. The absorbance may be determined with or withoutconsideration given to reflection and scattering. For convenience,influence exerted on the absorbance by reflection and scattering will bedisregarded in the following example.

As can be seen in the graph, the absorbance of each ink 103 varies thewavelength of light. In other words, the amount of heat generated ineach ink 103 irradiated with light (e.g., UV rays) varies with thewavelength of light. There is no uniformity among the inks 103 ofdifferent colors in terms of the way in which the absorbance (the amountof heat) varies. The color differences among the inks 103 arise fromdifferences in the material and/or content (mass %) of the coloringagent 107. When the material and/or content of the coloring agent 107 isnot uniform among the inks 103, the amount of heat generated by UVirradiation varies from ink to ink. The illustrated example suggeststhat in terms of the UV absorbance at the wavelength λ1, the black inkis on top, second is the cyan ink, followed by the yellow ink and themagenta ink, which exhibit a low absorbance. In this case, the black inkcan be heated excessively; conversely, the yellow ink and the magentaink can be heated insufficiently.

As a workaround, a UV-absorbing agent other than the coloring agent 107may be added to at least one of the inks 103 included in the ink set.This is an approach for enabling the inks 103 of different colors toachieve the same level of heating value through UV irradiation (emissionof UV rays of a predetermined wavelength) from the melting device 11.For example, the UV-absorbing agent other than the coloring agent 107may be added in such a manner that the percentage of the UV-absorbingagent in at least one of the inks 103 is not equal to the percentagecontent of another ink 103, which does not necessarily contain theUV-absorbing agent. With this approach, the percentage content of theUV-absorbing agent may be adjusted in such a way as to reduce thedifferences among the inks 103 in the amount of heat generated throughUV irradiation from the melting device 11.

When at least two inks 103 are irradiated with UV rays emitted by themelting device 11, the coloring agent 107 contained in one of the inks103 may have a lower UV absorptance than the coloring agent 107contained in the other ink 103. The percentage content of theUV-absorbing agent in one of the inks 103 may be higher than thepercentage content of the UV-absorbing agent in the other ink 10, whichdoes not necessarily contain the UV-absorbing agent. The magnituderelationship of the absorptance of the coloring agent 107 may beinterpreted as the magnitude relationship of the molar absorptioncoefficient (molar extinction coefficient) of the coloring agent 107.Alternatively, the magnitude relationship of the absorptance of thecoloring agent 107 may be interpreted as the magnitude relationship ofthe absorptance between solutions of similar concentrations, where thecoloring agent 107 is dispersed in solvent (e.g., water). The value ofthe molar absorption coefficient mentioned above is specific to thecoloring agent 107, and there is not much difference among the inks 103in terms of the concentration of the coloring agent 107. With thisapproach concerning the ink set, the percentage content of theUV-absorbing agent may be adjusted in such a way as to further reducethe differences among the inks 103 in the amount of heat generatedthrough UV irradiation from the melting devices 11.

Given that the inks 103 are to be irradiated with UV rays emitted by themelting device 11, the percentage content of the UV-absorbing agent maybe adjusted in such a manner that the ink 103 containing a coloringagent with a lower UV absorptance has a higher content of UV-absorbingagent. When the two inks 103 are irradiated with UV rays emitted by themelting device 11, one of the inks 103 may have a lower UV absorptanceof the coloring agent 107 than the other ink 103. The percentage contentof the UV-absorbing agent in one of the inks 103 may be higher than thepercentage content of the UV-absorbing agent in the other ink 103, whichdoes not necessarily contain the UV-absorbing agent. The absorptance maybe interpreted as the absorbance or a value (the absorption coefficient)determined by dividing the absorbance by the length of a sample (ink)upon which UV rays are incident. The UV absorptance of the coloringagent 107 contained in the ink 103 may be interpreted as the absorptanceof a sample in which the percentage content of the coloring agent 107 isequal to that in the ink 103 given that UV rays are not substantiallyabsorbed by other constituents (e.g., the medium 105) of the sample.Alternatively, the UV absorptance may be interpreted as the UVabsorptance of any of the inks 103 mentioned above in relation to thevariations given that the UV-absorbing agent is substituted by the sameamount of the medium 105. The absorptance may be measured by using awell-known spectrophotometer. With this approach concerning the ink set,the percentage content of the UV-absorbing agent may be adjusted in sucha way as to further reduce the differences among the inks 103 in theamount of heat generated through UV irradiation from the melting device11.

When the melting device 11 emits UV rays covering a relatively broadrange of wavelength, the expression “UV rays emitted by the meltingdevice 11” with regard to the comparisons made on the UV absorptance orthe like may be interpreted as UV rays at a representative wavelength inthe range concerned. The representative wavelength may be set asappropriate. UV rays emitted by the melting device 11 may be presentedin a form of a spectrum with the horizontal and vertical axesrepresenting the wavelength and the energy, respectively. Therepresentative wavelength may be the center wavelength (the midpoint oflower and upper wavelength limits) in a range in which energy at a levelof statistical significance is obtained. Alternatively, therepresentative wavelength may be the wavelength at which the peak energyis obtained. Still alternatively, the representative wavelength may bethe wavelength at which the integral of the energy in the wavelengthrange with energy at a level of statistical significance is bisectedinto a high frequency side and a low frequency side.

FIG. 12B schematically illustrates an ink set including the inks 103 towhich the UV-absorbing agent is added as in the example described above.

For greater clarity, the fixing polymer 109 and the like (constituentsof the ink 103 other than the medium 105, the coloring agent 107, and aUV-absorbing agent 113) are not illustrated in FIG. 12B. K, C, Y, and Min FIG. 12B denote black, cyan, yellow, and magenta, respectively.

FIG. 12B illustrates an example in which UV rays at the wavelength λ1(see FIG. 12A) are emitted. The ink 103 in black is on top in terms ofthe heating value at the wavelength λ1 and does not contain theUV-absorbing agent 113. The ink 103 in cyan contains the UV-absorbingagent 113. The ink 103 in yellow and the ink 103 in magenta are thelowest in terms of the heating value at the wavelength λ1 and each havea higher percentage content of the UV-absorbing agent 113 than the ink103 in cyan.

FIG. 13A is a graph schematically illustrating light absorptionproperties of the UV-absorbing agent 113 in an example. The horizontalaxis and the vertical axis of the graph in FIG. 13A are identical to therespective axes of the graph in FIG. 12A.

As can be seen in the graph, the UV-absorbing agent 113 exhibits a risein absorbance. The wavelengths at which the rise is exhibited issubstantially within a range denoted by RU. The UV-absorbing agent 113has little influence on visible light (visibility of the ink 103) whileUV rays absorbed by the UV-absorbing agent 113 generate a large amountof heat. The (maximum value of the) absorbance in a range denoted by RVis not more than 10% or not more than 5% of the peak value of theabsorbance or of the absorbance at the wavelength (λ1) of UV raysemitted by the melting device 11.

FIG. 13B is a graph schematically illustrating light absorptionproperties of the inks 103 in an example. The inks 103 concerned arethose mentioned above as the variations and contain the UV-absorbingagent 113. The horizontal axis and the vertical axis of the graph inFIG. 13B are identical to the respective axes of the graph in FIG. 12A.As in FIG. 12A, LY, LM, LC, and LK denote the respective linesrepresenting the four colors.

As described above with reference to FIG. 12B, inks of different colorscan achieve the same level of absorbance (absorptance). Morespecifically, the UV-absorbing agent 113 having characteristicsillustrated in FIG. 13A are added to inks such that inks of differentcolors exhibit the same level of absorbance (absorptance) at thewavelength (λ1) of UV rays emitted by the melting device 11. For all thecolors, the difference in absorptance (the difference between thehighest absorptance and the lowest absorptance) at the wavelength λ1 isnot more than 50%, not more than 20%, or not more than 10% of thehighest absorptance. It is only required that for at least two inks 103of different colors in the variations concerning the ink set, thedifference in the absorptance at the wavelength λ1 be reduced to someextent by the addition of the UV-absorbing agent 113. Unlike the exampleillustrated in FIG. 13B, not all the inks in another example have thesame level of absorptance at the wavelength λ1.

The UV-absorbing agent 113 may be in any desired form. For example, asubstance that can be used to protect a polymer or a coloring agent or asubstance that can be contained in cosmetics may be used as theUV-absorbing agent 113. Examples of such a UV-absorbing agent includedihydroxybenzophenone compounds, benzotriazole compounds,hydroxyphenyltriazine compounds, and cyanoacrylate compounds.

As mentioned above in relation to the first embodiment, the ink ejector7 may eject two inks 103 containing different coloring agents 107. Asmentioned above in relation to the variations, the UV absorptance of thecoloring agent 107 contained in one of the two inks 103 (e.g., Y or M)may be lower than the UV absorptance of the other coloring agent 107contained in the other ink (e.g., C or K), and the mass % of theUV-absorbing agent 113 different from the coloring agents 107 may behigher in one of the two inks 103 than in the other ink 103.

This feature reduces the variability between the inks 103 of differentcolors in the amount of heat generated per unit time under UVirradiation at the predetermined wavelength λ1 and, as a result, reducesthe possibility that the ink 103 of a specific color will be heatedexcessively or insufficiently. Thus, the inks 103 on the object 101 canbe fixed with stability, irrespective of (the color scheme of) an imageprinted on the object 101.

The technique disclosed herein is not limited to the embodimentsdescribed above and may be implemented in various forms.

It is not required that the object on which a printed record is to beproduced be long and/or be conveyed by at least one roller. For example,the printing apparatus may run a conveyor belt such that the objectplaced on the conveyor belt is conveyed. In this case, the object may becut-sheet paper, cut pieces of cloth, lumber, or tiles.

It is not required that the conveyor that conveys the object be includedin the printing apparatus. That is, it is not required that thedirection of conveyance of the object, the upstream side in thedirection of conveyance, and the downstream side in the direction ofconveyance be specified. For example, the printing apparatus may causevarious devices (the dryer, the ink ejector, the melting device, and/orthe auxiliary melting device) to shift when the object is stationary.More specifically, printing may be performed by using a robot that movesthe ink ejector along the surface of the object. Before the ink ejectoris brought close to the object or after the ink ejector is retracted, awarm air dryer fixed to the printing apparatus or carried by the robotmay eject a jet of warm air to cause the medium to evaporate. After theink ejector is retracted, the melting device may be brought close to thesurface of the object by the robot to cause the fixing polymer to melt.In such an embodiment, printing may be performed not onlytwo-dimensionally but also three-dimensionally by moving the ink ejectoralong surfaces of an object having a three-dimensional shape. Variousdevices may be moved while the object is conveyed. In some embodiments,the expression “direction of conveyance of the object” may be read asthe direction in which the object and various devices shift relative toeach other.

Examples of the dryer are not limited to the heat rollers and the warmair dryer. For example, the dryer may irradiate the object with infraredrays to heat the object. As mentioned above in relation to theembodiments, it is not required that the dryer be located upstream anddownstream of the ink ejector; that is, the dryer may be in positionalagreement with the ink ejector. For example, the dryer may include aplate-like heater that faces the ink ejector with the objecttherebetween. In this state, the plate-like heater is in contact withthe back surface of the object.

The embodiments described above each involve the use of the second dryerdisposed between the ink ejector and the melting device or the use ofthe auxiliary melting device that faces the melting device with theobject therebetween. Examples of the second dryer include the onedenoted by 17B in FIG. 9 and those denoted by 455A and 455B in FIG. 11 .Examples of the auxiliary melting device include those denoted by 17B inFIGS. 1 and 10 , respectively. In some embodiments, the printingapparatus includes both the second dryer and the auxiliary meltingdevice.

1. A printing apparatus comprising: an ink ejector configured to ejectan ink to an object on which a printed record is to be produced, the inkcontaining a medium and a fixing polymer; a dryer configured to heat theobject to expedite evaporation of the medium; and a melting deviceconfigured to irradiate the ink on the object with ultraviolet rays tosubject the ink to heat that causes the fixing polymer to melt and tofix the ink to the object accordingly.
 2. The printing apparatusaccording to claim 1, wherein the melting device is disposed downstreamof the dryer in a direction of conveyance of the object.
 3. The printingapparatus according to claim 1, wherein the melting device causes thefixing polymer to melt after the dryer causes the medium to evaporate.4. The printing apparatus according to claim 1, wherein an amount ofheat to be applied to the object by the dryer, relative positions of thedryer and the melting device, and a speed of conveyance of the objectare set to values at which the medium fully evaporates through theapplication of heat by the dryer before the melting device causes thefixing polymer to melt.
 5. The printing apparatus according to claim 1,further comprising an auxiliary melting device located opposite themelting device with the object placed between the auxiliary meltingdevice and the melting device, the auxiliary melting device beingconfigured to heat a back surface of the object to aid in melting of thefixing polymer, the back surface being opposite to a surface of theobject to which the ink is ejected.
 6. The printing apparatus accordingto claim 5, wherein the auxiliary melting device has a heating surfacemaintained at a predetermined temperature during contact with the backsurface of the object, and the melting device heats the ink on theobject to a temperature above the predetermined temperature.
 7. Theprinting apparatus according to claim 1, wherein the dryer comprises afirst dryer and a second dryer disposed upstream and downstream,respectively, of the ink ejector in a direction of conveyance of theobject, and the melting device is disposed downstream of the seconddryer.
 8. The printing apparatus according to claim 1, furthercomprising a conveyor configured to convey the object and to bend atleast part of the object being conveyed, to provide a surface of theobject that is curved convexly and to which the ink is ejected, whereinthe melting device emits ultraviolet rays to a region of the objectbeing bent by the conveyor.
 9. The printing apparatus according to claim1, wherein a plurality of light sources constituting the melting device,and the plurality of light sources are configured to emit ultravioletrays of different wavelengths.
 10. The printing apparatus according toclaim 1, wherein the dryer comprises a first portion and a secondportion designed to repeatedly come into contact with the object in analternating manner to heat the object.
 11. The printing apparatusaccording to claim 1, wherein the dryer heats the object to atemperature below a glass-transition temperature of the fixing polymer,and the melting device heats the ink on the object to a temperatureequal to or higher than the glass-transition temperature of the fixingpolymer.
 12. The printing apparatus according to claim 11, wherein theink contains a first polymer different from the fixing polymer, and thedryer heats the object to a temperature equal to or higher than aglass-transition temperature of the first polymer and lower than theglass-transition temperature of the fixing polymer.
 13. The printingapparatus according to claim 12, wherein the dryer comprises a firstdryer disposed upstream of the ink ejector in a direction of conveyanceof the object, and an amount of heat to be applied by the first dryer,relative positions of the first dryer and the ink ejector, and a speedof conveyance of the object are set to values at which a temperature ina region of the object immediately anterior to a region of the objectfacing the ink ejector is equal to or higher than the glass-transitiontemperature of the first polymer and lower than the glass-transitiontemperature of the fixing polymer.
 14. The printing apparatus accordingto claim 12, wherein the dryer is disposed upstream of the meltingdevice in a direction of conveyance of the object, and an amount of heatto be applied by the dryer, relative positions of the dryer and themelting device, and a speed of conveyance of the object are set tovalues at which a temperature in a region of the object extending fromimmediately posterior to the dryer to immediately anterior to a regionof the object facing the melting device is equal to or higher than theglass-transition temperature of the first polymer and lower than theglass-transition temperature of the fixing polymer.
 15. The printingapparatus according to claim 12, wherein the first polymer is adispersant polymer.
 16. The printing apparatus according to claim 12,wherein the glass-transition temperature of the fixing polymer is higherthan a glass-transition temperature of any other polymer contained inthe ink.
 17. The printing apparatus according to claim 1, wherein theink ejector ejects at least two kinds of the ink containing differentcoloring agents, and a percentage content of an ultraviolet-absorbingagent in one ink of the at least two kinds of the ink is not equal to apercentage content of the ultraviolet-absorbing agent in another ink ofthe at least two kinds of the ink, with the ultraviolet-absorbing agentbeing different from the different coloring agents.
 18. The printingapparatus according to claim 17, wherein when the at least two kinds ofthe ink are irradiated with ultraviolet rays emitted by the meltingdevice, a coloring agent of the different coloring agents contained inthe one ink has a lower ultraviolet absorptance than a coloring agent ofthe different coloring agents contained in the other ink, and thepercentage content of the ultraviolet-absorbing agent in the one ink ishigher than the percentage content of the ultraviolet-absorbing agent inthe other ink.
 19. The printing apparatus according to claim 17, whereinwhen the at least two kinds of the ink are irradiated with ultravioletrays emitted by the melting device, the one ink has a lower ultravioletabsorptance of the coloring agent than the other ink, and the percentagecontent of the ultraviolet-absorbing agent in the one ink is higher thanthe percentage content of the ultraviolet-absorbing agent in the otherink.